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Science of Dry Shampoo: The Dirty Details

What is in your dry shampoo?

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As the week passes and our schedules get busier we often use dry shampoo to tame our tresses before the next wash. When reaching for that candy-colored aerosolized spray, rarely do we stop to consider the possible ingredients of the spray and instead give the hair an extra fluff and continue with our day. Fear not, we have unmasked several of the ingredients in dry shampoo and how they can affect the skin.

 

The Normal Scalp Produces Oil

The external barrier of the skin is comprised of a layer of dead cells called the stratum corneum.[1] The membranes of these cells are lipid (fat) enriched, with 50% ceramides, 25% cholesterols, and 15% free fatty acids.[2] The ceramides, cholesterol, and free fatty acid are produced to help minimize water loss.[2] In addition to protection, the multiple layers of skin on the scalp contain hair follicles and can be disrupted by friction like everyday grooming and brushing.[3-5] Sebaceous glands (the skin’s oil glands) on the scalp and other hair-bearing areas of skin produce lipids like 18-methyl-eicosanoic acid that help lubricate and waterproof the hair.[6,7] 

The hair follicles are divided into three layers:

  • Cuticle (outer layer): The cuticle of the hair is the external layer of the hair and contains the water-repellant molecule 18-methyl-eicosanoic acid[5]
  • Cortex (middle layer): The cortex of the hair follicle, located between the cuticle and the medulla, forms the major part of the hair and is connected to the cell membrane complex[5,8]
  • Medulla (inner layer): The medulla region of the hair follicle is the innermost layer and usually is the area of split ends[3,4]

Hair follicles schematic with sebaceous glands

Hair follicles schematics with outer cuticle layer, middle cortex layer, and inner medulla layer. Epi= epidermis, SB = sebaceous glands, ORS = outer root sheath, HB = hair bulb
Credit: Tobin DJ, Int J Tricholog, 2009 

Shampoo to Help Hair

Hair can be damaged easily by everyday activities. Most shampoos are designed to prevent hair damage by reducing friction and water absorption of hair. The main four ingredients in a wet shampoo are: [9]

Table 1 – Wet Shampoo Ingredients

Shampoo Ingredient

Benefit

Cleansing Agent

Reduce buildup of skin and other products

Conditioning Agent

Give softness, gloss, disentangle hair

Special Care

Dandruff and greasy hair treatment

Additives

Stability and comfort of the product

 

 

Dry Shampoo Absorbs “Grease”

While wet shampoo can be helpful to the scalp, finding the time to fully wash hair can be difficult for many. Enter dry shampoo. The intention of dry shampoo is to absorb oils from the scalp and reduce the amount absorbed by the hair, giving more of a matte look. Most of the dry shampoos available for purchase are aerosolized sprays or mousses. While well-intentioned, many of the dry shampoos can contain harmful ingredients for your health. Before deciding to go the route of a dry shampoo, make sure the ingredients will not aggravate your skin. Some of the common ingredients include:

Table 2 – Dry Shampoo Ingredients

Cornstarch

While cornstarch can have great oil absorption capabilities, be careful if it has had previous exposure to moisture, particularly as it can harbor fungi.[10-12] In a few cases, patients have had allergic reactions to cornstarch.[13]

Talc

While talc can help soak up the oily moisture of the scalp, one study has questioned its safety.[14]

Kaolin

Kaolin, also known as white clay, is an absorptive ingredient often used in ceramics and industrial products.[15]

Laminaria

Laminaria, more commonly known as kelp, is a brown algae known for its absorptive properties.[16] While it is effective at absorbing moisture, it can also effectively absorb heavy metals such as copper, zinc, and cadmium.[17]

Denatured alcohol

Alcohol can be drying to the skin, especially in those that already have dry skin.[18]

Liquefied Petroleum Gases

These ingredients can range from butane, isobutane, propane, and alcohol. Most often these are used as propellants and can be irritating to the skin.[19,20]

 

Even though the whole point of dry shampoo is to be an easy, leave-in product to soak up oil on the scalp, the ingredients can build up over time, leading to inflammation of the skin.[21]

 

Can Dry Shampoo Cause Dandruff?

Dandruff is usually related to three factors: Malassezia fungi infection, oil scalp production, and individual sensitivity.[22] This common condition develops through the overproduction of oil on the skin, which can lead to inflammation.[23] Individuals who are more prone to developing dandruff often have weakened stratum corneum layers.[24] While dry shampoo does not directly cause the fungal overgrowth seen in dandruff, it can potentially make the skin more susceptible to this condition through aiding in the accumulation of skin oils and drying out the skin. If your skin becomes irritated from using dry shampoos, contact your health care provider to help alleviate your symptoms.

 

* This Website is for general skin beauty, wellness, and health information only. This Website is not to be used as a substitute for medical advice, diagnosis or treatment of any health condition or problem. The information provided on this Website should never be used to disregard, delay, or refuse treatment or advice from a physician or a qualified health provider.

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References

 

 

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  2. Feingold KR, Elias PM. Role of lipids in the formation and maintenance of the cutaneous permeability barrier. Biochim Biophys Acta.2014;1841(3):280-294; PMID: 24262790 Link to research.
  3. Dawber R. Hair: its structure and response to cosmetic preparations. Clinics in dermatology.1996;14(1):105-112; PMID: Link to research.
  4. Kamath Y, Weigmann HD. Fractography of human hair. Journal of Applied Polymer Science.1982;27(10):3809-3833; PMID: Link to research.
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  7. Wertz PW, Downing DT. Integral lipids of human hair. Lipids.1988;23(9):878-881; PMID: Link to research.
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