Knowledge of hair grooming oils used in the hair and scalp can enhance patient care. This article reviews coconut, jojoba, argan, olive, tea tree, castor, miracle fruit seed oils, and shea butter.
The use of natural oils in hair grooming among African Americans is a central practice that dates back over 400 years ago, stemming from the practices of their African ancestors. Prior to the trans-Atlantic slave trade, palm oil and hand-carved wooden combs were used to soften and mold the hair of men and women into a range of styles, each carrying different aesthetic, social, and spiritual meanings among the various ethnicities across the African continent.1
When Africans were subjugated, their access to oils, herbs, and hair tools was stripped. Enslaved African Americans used whatever they could to maintain their hair. To reap the social and economic advantages of conforming to European beauty ideals, most blacks strived for straighter hair. The enslaved African Americans used oil-based substances, such as bacon fat, goose grease, or butter to soften the hair, prep it for straightening, and to add shine.1 After the substance was placed on the hair, a butter knife heated over a fire was used as a makeshift curling iron to straighten the hair. Men would employ the grease used for lubricating axle wheels as both a hair straightener and hair dye. A sheep fleece carding tool was used to untangle tightly-coiled hair. Cornmeal and kerosene were used to clean the scalp. Scalp infections such as ringworms and lice infections were common, leading to rashes and patchy baldness, which were often concealed with a scarf.1
In the early 1900s, with contributions of African Americans, such as businesswomen Annie Malone and Madame CJ Walker, the African American hair care industry was born. This ushered in the development and wide distribution of hair styling tools, as well as petroleum-based hair products. The hair pomades and hair greases consisted of petroleum, beeswax, and sulfur, and were effective in softening the hair and reducing scalp infections.1 Hair grease was used as a hairdressing with the straightening comb, or hot comb, to temporarily straighten tightly coiled hair. As thermal straightened hair usually reverts back to its curly texture when exposed to water, these thick, ointment-like oils were effective in maintaining straightened styles in humid conditions. As African Americans began to rely more on chemical straightening, the use of heavy petroleum/beeswax products was replaced with lighter oils that were liquid at room temperature, such as mineral oil.1
Over the last decade, natural hair (ie, hair shafts that have not been chemically altered) has grown in popularity in the African American community. With this change has come an ever-growing demand for natural oils for the purposes of hair grooming, maintaining moisture in the hair shafts, and preventing hair breakage. This article reviews oils commonly used in the hair and scalp, such as coconut, jojoba, argan, olive, tea tree, castor, and miracle fruit seed oils, as well as its cousin shea butter (Table). It is important for dermatologists to have knowledge of these commonly used oils in order to enhance patient care.
Coconut oil is an edible oil extracted from the meat of matured coconuts (Cocos nucifera).2 Historically it has been used as a hair grooming product in developing countries around the world, particularly in Africa and Asia, where coconuts are widely cultivated. Much of what is known about the properties of coconut oil on hair can be found in studies conducted in India, where its use is widespread. It can be found in multiple cosmetic formulations, including but not limited to most makeup preparations, shampoos, conditioners, lotions, baby oil/lotions, hair straighteners, nail products, suntan products, shaving products, cleansers, and deodorants.2
Coconut oil is a small, low-molecular-weight, hydrophobic substance comprised largely of triglycerides. Lauric acid, a polar fatty acid, makes up the majority of the fatty acid content, and greatly contributes to the positive charge of coconut oil.2 These structural components directly affect the unique cosmetic properties of coconut oil in hair grooming. When applied topically, coconut oil has the ability to penetrate deep into the hair shaft.
In a study by Ruetsch and colleagues, coconut oil was shown to be absorbed into the cortical layer of the hair shaft, when evaluated under secondary ion mass spectrometry.3 It was also shown to reduce the amount of swelling of hair submerged in water for an hour by 48%, when compared to hair that was uncoated with oil, suggesting that coconut oil is effective in protecting hair from hygral fatigue (the hair cuticle damage ensued from the swelling and contraction of hair fibers due to frequent wetting and drying).3 This is further supported in the study by Rele and Mohile, which showed that when used as a pre-wash conditioning treatment, coconut oil significantly reduced the amount of water retention and hair swelling (which raises the cuticle of the hair, rendering it vulnerable to mechanical damage), as well as protein loss incurred from wet combing.4 Finally, coconut oil, similar to mineral oil and many vegetable oils, is effective at maintaining moisture within a hair fiber.5
In a study conducted by Keis and colleagues, coconut oil applied to hair slowed the rate of moisture loss out of the hair shaft, similar to the effect of hair moisturizers. It also increased the retention of moisture within a hair shaft at relatively lower humidity levels, when compared to hair untreated with oils.5 It is likely that the small molecular structure and positive charge of hydrophobic coconut oil enables it to penetrate past the small openings of the cuticle layer, bind to the negatively charged hair fiber, and act as a water repellant within the fiber. When coating the hair shaft, it provides a hydrophobic barrier that locks in moisture.3
In a 2017 report compiled by the Cosmetics Ingredients Review Expert Panel, coconut oil and its derivatives were extensively discussed.6 Coconut oil and hydrogenated coconut oil were found to be relatively nontoxic by ingestion, and hydrogenated coconut oil was nontoxic, nonirritating, and not a sensitizer.6 Potassium cocoate, a derivative of coconut oil, was found to be irritating in 0.9% of participants in a study evaluating its skin irritating potential in individuals with preexisting dermatitis. Coconut oil, however, was not an allergen at 100% concentration in a separate double-blinded randomized-control pilot study of 12 participants.6 Although contact allergy to pure coconut oil is unlikely, mild irritant reactions and sensitization to coconut derivatives such as cocamidopropyl dimethylamine, coconut diethanolamide, cocamidopropyl betaine, and cocamidopropyl PG-dimonium chloride phosphate, have been documented (though none were from application to the scalp).7
Coconut oil is considered a comedogenic substance. Anecdotal reports of scalp irritation due to coconut oil have been reported on several layperson hair care websites,8,9 however, no such reports were documented in medical literature. Of note, cosmetic products labeled as coconut oil, or any oil, may not be in its purest form, and can possibly contain a number of unidentified additives that can give rise to an irritant or allergic contact dermatitis (ACD).
Article continues on page 2
Jojoba oil is a clear, golden liquid extracted from the seeds of the jojoba (Simmondsia chinensis) plant, which grows in the deserts of the southwestern United States and Mexico.10 It has been used as a skin lubricant and hair conditioner among the indigenous tribes of the Americas; commonly advertised as having similar properties to human sebum due to its composition of wax esters, its use as a hair and scalp conditioner has gained traction among African Americans who seek natural hair products,11,12 and is used as an ingredient in many hair and skin cosmetic products, including hair shampoos, conditioners, straighteners, hair dyes, face and eye makeup, fragrance products, baby products, personal hygiene products, nail care products, shaving products, suntan products, soaps, detergents, and various skin care products.13 Animal testing of jojoba liquid wax has demonstrated that it possesses anti-inflammatory properties.14 In vitro scratch wound experiments using human fibroblasts and keratinocytes demonstrated that jojoba liquid wax accelerated wound closure, suggesting its potential use in the treatment of wounds in clinical settings.15
Jojoba oil has been reported to cause contact dermatitis of the skin and scalp. A study reporting on suspected sensitivity to jojoba oil found that in 5 of 6 study participants, a positive reaction was observed during patch testing. The sixth participant, suspected of being sensitive to jojoba oil in a hair conditioner, did not react when a patch test was done on the forearm, but did develop a contact dermatitis of the scalp during 2 subsequent tests in which pure jojoba oil was applied directly to the scalp.16 A separate case of a patient with a history of several inhalant allergies was found to exhibit a delayed hypersensitivity reaction to jojoba seed powder,17 and a third case was reported in a patient sensitive to jojoba oil found in a moisturizer.18
Argan oil, derived from the fruit of the Argania spinosa tree, is native to the southwestern regions of Morocco and parts of Algeria. It has been used for hundreds of years by people in those regions to address a range of issues, including dry skin, wrinkles, joint pain, hair loss, infertility, and even heart disease. However, little clinical evidence exists to validate the wide range of use of argan oil.19 In hair, it is typically used as a dressing to impart shine and lubrication to the hair fiber. Argan oil is rich in linoleic acid, vitamin E, and oleic acid, which contributes to its ability to penetrate skin, reduce dryness, and possibly mitigate or prevent inflammation.19 Argan oil can be found in an array of cosmetic preparations, including hair shampoos, conditioners, straighteners, hair dyes, face and eye makeup, fragrance products, baby products, personal hygiene products, nail care products, shaving products, suntan products, soaps, detergents, and various skin care products.6
Argan oil applied to hair shafts as a post-dye treatment was found effective in reducing the sustained protein loss in hair that underwent hair coloring, suggesting that it is protective against the damage caused to hair from dyeing. It is possible that argan oil exhibits these effects due to the penetration of the oil into the strands, similar to the behavior of coconut oil, however, studies to show the ability of argan oil to penetrate the hair shaft were not found in the literature.20
Although rarely reported, the allergenicity of argan oil has been documented. Argan oil has been reported to induce rhinitis and conjunctivitis in a male exposed to the smell of argan oil. He later developed anaphylaxis from ingestion of the oil. The allergy was confirmed with positive prick tests to argan oil and argan paste.21
Castor oil is derived from the seeds of the Ricinus communis plant and its main constituent, ricinoleic acid. Outside of cosmetics, it has been used as a medicinal purgative and an industrial lubricant. It is often included in various cosmetic products, including hair shampoos, conditioners, straighteners, hair dyes, face and eye makeup (especially lipsticks), fragrance products, baby products, personal hygiene products, nail care products, shaving products, suntan products, soaps, detergents, and various skin care products.22 It is used as an emulsion stabilizer, surfactant, and skin-conditioning agent in cosmetics.22 Castor oil is often used to soften hair during hair grooming, for hot oil/deep conditioning hair treatments, and to seal in moisture on freshly washed hair.
Individuals experiencing thinning hair secondary to androgenic or traction alopecia frequently turn to castor oil in an attempt to achieve hair regrowth.23 Castor oil is commonly applied to eyebrows, eyelashes, and the temporal regions of the scalp, for the purpose of promoting the growth and thickening of hair strands in those areas. Due to the high viscosity of the oil, castor oil makes hairs to appear thicker when applied topically. While it is lauded as a hair growth agent throughout the internet, there is no scientific evidence that the topical application of castor oil is effective in regrowing thinning hair, or in permanently thickening the hair of the eyelashes, eyebrows, or any hair on the body.
Figure. Castor oil has been documented to cause acute hair felting/matting, or bird’s nest hair. Photo courtesy—Wake Forest Baptist Health Department of Dermatology.
The Cosmetics Ingredients Review Expert Panel reported that castor oil is not a significant skin irritant, sensitizer, or photosensitizer in human clinical tests, but patients with occupational dermatoses may have a positive reaction to castor oil or ricinoleic acid.22 Of note, several case reports of ACD to castor oil found in deodorants,24 lipsticks,25,26 makeup removers,27 cerumenolytics,28,29 and wart removers,30 have been documented. Thus, in patients that present with contact dermatitis, castor oil should be tested along with other skin sensitizers. Additionally, castor oil has been documented to cause acute hair felting/matting, or bird’s nest hair (Figure).31
Olive oil is a liquid fat extracted from olives (Olea europaea), a plant that has naturally been found near the Mediterranean since the 8th millennium bc. It is made up of several lipids, including oleic acid, stearic, arachidic, linoleic, and palmitic acids. In addition to its extensive culinary uses, olive oil is also used in many cosmetic and pharmaceutical products. It is included in a wide variety of cosmetic preparations, including hair shampoos, conditioners, straighteners, hair dyes, face and eye makeup, fragrance products, baby products, personal hygiene products, nail care products, shaving products, suntan products, soaps, detergents, and various skin care products.6 On the hair, it has been said to prevent dandruff, treat cradle cap, strengthen and grow hair, and even prevent hair loss through preventing the production of dihydrotestosterone (DHT).32,33
There is no scientific evidence that supports the idea that olive oil can prevent hair loss by reducing DHT production. In addition, its use as treatment for cradle cap should be used with caution, as olive oil can potentially exacerbate it. Malassezia species actually feed on saturated fatty acids, and a medium containing saturated and unsaturated fatty acids, such as olive oil, can lead to the overgrowth of Malassezia; excessive accumulation of unsaturated fatty acid by-products on the scalp can lead to scaling and inflammation. Olive oil is a standard in vitro culture media for Malassezia.34
Olive oil is considered to be a weak irritant and a low-risk sensitizer, though its actual allergenic components are not known. With a high level of oleic acid and a low level of linoleic acid, olive oil can disrupt the skin barrier, decreasing the thickness and integrity of the stratum corneum.35 Several case reports of positive patch testing for olive oil have been described in patients with an occupational exposure, a form of dermatitis or lesion, or venous eczema. Investigations into whether reactions to olive oil were due to irritation vs contact sensitization concluded that olive oil was a weak irritant, and not a contact sensitizer.6
Tea Tree Oil
Tea tree oil is an essential oil extracted from the Melaleuca alternifolia plant of the Myrtaceae family. It is native to the coast of northeastern Australia. A holy grail of natural cosmetics, tea tree oil is widely known for its antiviral, antifungal, and antiseptic properties.36 It is often added to a number of cosmetic products, including shampoos, conditioners, body lotion, hand/face washes, deodorants, soaps, and foot sprays/powders.37 One study found that 5% tea tree oil shampoo produced statistically significant improvements on a quadrant-area severity scale, as well as patient reported scores of scaliness, itchiness, and greasiness.38 The incidence of ACD due to tea tree oil (and several other essential oils) is increasingly being acknowledged. One review found that tea tree oil was among 79 essential oils to cause ACD.39 Tea tree oil was again identified in a review on fragrance ACD.40
The prevalence of ACD due to tea tree oil is approximately 1.4%.36 Tea tree oil consists of more than 100 distinct compounds and is often mislabeled, or does not meet the guidelines of the International Organization for Standardization. Thus, it has been challenging to thoroughly evaluate tea tree oil as a contact allergen. When possible, patch testing using the patient’s supply of tea tree oil is advised.41
Miracle Fruit Oil
Miracle fruit (Synsepalum dulcificum) seed oil, is a fruit oil derived from the miracle fruit berry, found in several parts of West Africa. It is comprised of a number of fatty acids, including 42% palmitic acid and 1.5% squalene. The miracle fruit is mostly known for its taste modifying properties and used in several African cuisines as a natural sweetener.42 While use of this oil as a hair grooming product is not a common practice, there is evidence that as a hair oil, it may be effective in improving the health of the hair.
One study showed that miracle fruit seed oil was more effective at reducing hair breakage over an 8-month period compared with argan oil. This is likely due to the composition of the oil, having a 1:1 saturated/unsaturated fatty acid ratio, which allows it to both effectively penetrate the hair shaft, and provide external lubrication.42
Shea butter is an ivory-colored fat extracted from the nut of the African Shea tree, known as Vitellaria paradoxa, or Butryspermum paradoxum, or B parkii). It grows throughout the savanna belt of West Africa and has been used in African countries both as a cosmetic agent and a cooking oil. Shea butter is comprised of 40% to 60% oleic acid, 20% to 50% stearic acid, as well as linoleic, palmitic, linolenic, and arachidic acid.43 It is included in a wide array of cosmetic formulations, including hair shampoos, conditioners, straighteners, hair dyes, face and eye makeup, fragrance products, baby products, personal hygiene products, nail care products, shaving products, suntan products, soaps, detergents, and various skin care products.6 The use of shea butter as a skin emollient and a hairdressing agent is popular among people of African descent. Because it is solid at room temperature, raw, unrefined shea butter is quite thick, and difficult to spread. It is conventionally used as a thick moisturizer and a heavy-duty moisture sealant for hair. It is also favored hairdressing in heat-free stretching of highly-textured African hair.43
A number of studies have reviewed the dermal effects of shea butter on both animals and humans. On a study of 3 white rabbits, shea butter was applied onto the skin and occluded for 4 hours. Two of the rabbits exhibited mild erythema with or without edema, which resolved by day 3 or 4.44 A second study on guinea pigs demonstrated no evidence of delayed hypersensitivity.6 Shea butter in several cosmetic formulations were tested, and none were found to cause irritation or sensitization in human subjects.6
The use of butters as a hairdressing agent is effective at retaining moisture, however, thick butters should be avoided in hair combing. One study evaluating the use of several Brazilian butters and liquid oils in hair grooming found that while liquid oils reduced the combing force on wet hair, thick butters increased them.45 This can lead to increased mechanical damage, including the formation of split ends. While shea butter was not among the butters in this study, all thick butters studied shared this property.45
The use of vegetable oils is extremely common throughout the world. There are few studies that thoroughly assess the interaction of these oils with human hair or scalp skin. The current knowledge surrounding their use is drawn from a few studies performed primarily on coconut and mineral oil. Generally, vegetable oils are safe for topical use. However, anecdotal testimonials from hair care websites show that these products are more irritating than reported in the literature, suggesting a need for further evaluative studies that can better characterize the dermal effects of hair oils on the scalp. Efficacy for the multitude of conditions for which they are used, including seborrheic dermatitis, psoriasis, hair breakage/fragility, pruritus of the scalp, and providing luster, is difficult to prove, as there are few studies performed to date.
Dr Uwakwe is a research fellow in the department of dermatology at Wake Forest Baptist Health in Winston-Salem, NC.
Dr McMichael, The Mane Point Section Editor, is professor and chair in the department of dermatology at Wake Forest Baptist Health in Winston-Salem, NC.
Disclosure: Dr McMichael has received grants from Allergan and Proctor & Gamble. She is a consultant for Allergan, eResearch Technology, Inc, Galderma, Guthey Renker, Johnson & Johnson, Keranetics, Merck & Co, Inc, Merz Pharmaceuticals, Proctor & Gamble, Samumed, and Incyte. She receives royalties from Informa Healthcare and UpToDate and also has conducted research for Samumed.
Dr Uwakwe reports no relevant financial relationships.
1. Byrd AD, Tharps LL. Hair Story: Untangling the Roots of Black Hair in America. New York, NY: St. Martin’s Press; 2001.
2. Burnett CL, Bergfeld WF, Belsito DV, et al. Final report on the safety assessment of Cocos nucifera (coconut) oil and related ingredients. Int J Toxicol. 2011;30(3 suppl):5S-16S.
3. Ruetsch SB, Kamath YK, Rele AS, Mohile RB. Secondary ion mass spectrometric investigation of penetration of coconut oil and mineral oils into human hair fibers: relevance to hair damage. J Cosmet Sci. 2001;52(3):169-184.
4. Rele AS, Mohile RB. Effect of mineral oil, sunflower oil, and coconut oil on prevention of hair damage. J Cosmet Sci. 2003;54(2):175-192.
5. Keis K, Huemmer CL, Kamath YK. Effect of oil films on moisture vapor absorption on human hair. J Cosmet Sci. 2007;58(2):135-145.
6. Burnett CL, Fiume MM, Bergfeld WF, et al. Safety assessment of plant-derived fatty acid oils. Int J Toxicol. 2017;36(3_suppl):51S-129S.
7. Gupta D, Thappa DM. Dermatoses due to Indian cultural practices. Indian J Dermatol. 2015;60(1):3-12.
8. White W. Popular hair vlogger naptural85 reveals coconut oil is not life. BlackDoctor website. https://blackdoctor.org/506788/popular-hair-vlogger-naptural85-reveals-coconut-oil-is-not-life/. Accessed April 28, 2018.
9. Could my coconut oil be the cause of my sore and irritated scalp? Long Hair Care Forum website. https://longhaircareforum.com/threads/could-my-coconut-oil-be-the-cause-of-my-sore-and-irritated-scalp.461514/. Accessed April 28, 2018.
10. Wisniak J. Jojoba oil and derivatives. Prog Chem Fats Other Lipids. 1977;15(3):167-218.
11. Similar to skin sebum. Only Natural & Organics website. https://www.onlynaturalorganics.com.au/Blog/Similar-to-skin-sebum.aspx. Accessed April 28, 2018.
12. How I use shea butter and jojoba, ayurvedic and castor oil in my waist length 4B/4C hair regimen. BGLH website. https://bglh-marketplace.com/2015/04/how-i-use-shea-butter-and-jobjoba-ayurvedic-and-castor-oils-in-my-waist-length-4b4c-hair-regimen/. Accessed April 28, 2018.
13. Becker LC, Bergfeld WF, Belsito DV, et al. Safety assessment of simmondsia chinensis (jojoba) seed oil, simmondsia chinensis (jojoba) seed wax, hydrogenated jojoba oil, hydrolyzed jojoba esters, isomerized jojoba oil, jojoba esters, simmondsia chinensis (jojoba) butter, jojoba alcohol, and synthetic jojoba oil. https://www.cir-safety.org/sites/default/files/115_buff3f_suppl.pdf. Published September 23, 2008. Accessed April 28, 2018.
14. Habashy RR, Abdel-Naim AB, Khalifa AE, Al-Azizi, MM. Anti-inflammatory effects of jojoba liquid wax in experimental models. Pharmacol Res. 2005;51(2):95-105.
15. Ranzato E, Martinotti S, Burlando B. Wound healing properties of jojoba liquid wax: an in vitro study. J Ethnopharmacol. 2011;134(2):443-449.
16. Scott MJ, Scott MJ Jr. Jojoba oil. J Am Acad Dermatol. 1982;6(4 Pt 1):545.
17. Di Berardino L, Di Berardino F, Castelli A, Della Torre F. A case of contact dermatitis from jojoba. Contact Dermatitis. 2006;55(1):57-58.
18. Wantke F, Hemmer W, Götz M, Jarisch R. Contact dermatitis from jojoba oil and myristyl lactate/maleated soybean oil. Contact Dermatitis. 1996;34(1):71-72.
19. Monfalouti HE, Guillaume D, Denhez C, Charrouf Z. Therapeutic potential of argan oil: a review. J Pharm Pharmacol. 2010;62(12):1669-1675.
20. Faria PM, Camargo LN, Carvalho RSH, et al. Hair protective effect of argan oil (Argania spinosa kernel oil) and cupuassu butter (Theobroma grandiflorum seed butter) post treatment with hair dye. JCDSA. 2013;3(3A):40-44.
21. Astier C, Benchad Yel A, Moneret-Vautrin DA, Bihain BE, Kanny G. Anaphylaxis to argan oil. Allergy. 2010;65(5):662-663.
22. Cosmetic Ingredient Review Expert Panel. Final report on the safety Assessment of ricinus communis (castor) seed oil, hydrogenated castor oil, glyceryl ricinoleate, glyceryl ricinoleate SE, ricinoleic acid, potassium ricinoleate, sodium ricinoleate, zinc ricinoleate, cetyl ricinoleate, ethyl ricinoleate, glycol ricinoleate, isopropyl ricinoleate, methyl ricinoleate, and octyldodecyl ricinoleate. Int J Toxicol. 2007;26 suppl 3:31-77.
23. Lukas E. Can castor oil really help your hair grow? InStyle website. Published July 11, 2017. http://www.instyle.com/hair/can-castor-oil-for-hair-eyebrow-eyelash-growth. Accessed April 28, 2018.
24. Taghipour K, Tatnall F, Orton D. Allergic axillary dermatitis due to hydrogenated castor oil in a deodorant. Contact Dermatitis. 2008;58(3):168-169.
25. Sowa J, Suzuki K, Tsuruta K, Akamatsu H, Matsunaga K. Allergic contact dermatitis from propylene glycol ricinoleate in a lipstick. Contact Dermatitis. 2003;48(4):228-229.
26. Andersen KE, Nielsen R. Lipstick dermatitis related to castor oil. Contact Dermatitis. 1984;11(4):253-254.
27. Brandle I, Boujnah-Khouadja A, Foussereau J. Allergy to castor oil. Contact Dermatitis. 1983;9(5):424-425.
28. Sánchez-Guerrero IM, Huertas AJ, López MP, Carreño A, Ramirez M, Pajarón. Angioedema-like allergic contact dermatitis to castor oil. Contact Dermatitis. 2010:62(5):318-319.
29. Caralli ME, Seoane Rodríguez M, Rojas Pérez-Ezquerra P, Pelta Fernández R, De Barrio Fernández M. Palpebral angioedema and allergic contact dermatitis caused by a cerumenolytic. Contact Dermatitis. 2015;73(6):376-377.
30. Tabar A, Muro MD, Quirce S, Olaguibel JM. Contact dermatitis due to sensitization to lactic acid and castor oil in a wart remover solution. Contact Dermatitis. 1993;29(1):49-50.
31. Maduri VR, Vedachalam A, Kiruthika S. “Castor oil” – the culprit of acute hair felting. Int J Trichology. 2017;9(3):116-118.
32. Thrive Market. Olive oil and hair care. Huffington Post website. https://www.huffingtonpost.com/thrive-market/olive-oil-and-hair-care_b_10972790.html. Published July 29, 2016. Updated December 6, 2017. Accessed April 28, 2018.
33. Magnesi J. How to Treat Dry Patches Along Your Hairline. Leaftv website. http://www.ehow.com/way_5690045_olive-oil-remedies-dandruff.html. Accessed April 30, 2018.