Commonly Used Natural Oils in Hair Grooming
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.
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