Science of Dry Shampoo: The Dirty Details

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 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]

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 these products 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:

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.