Many shampoos and conditioners on the market now claim to combat hair loss, boost growth, and even prevent graying. However, a leading trichologist suggests that while some ingredients can improve hair's appearance, robust scientific evidence for significant growth from shampoos is often lacking.
Eva Proudman, a trichologist with two decades of experience and founder of UK Hair Consultants, explained that while medications like minoxidil and finasteride are scientifically proven to stimulate hair growth, most over-the-counter products offer more subtle benefits.
"The only compounds proven to make hair grow are medications like monoxidil and finasteride," Proudman stated. "But there are plenty of products that can boost thickness to make hair appear full."
Ingredients frequently found in hair-boosting products include peptides, niacinamide, caffeine, biotin (vitamin B7), and rosemary oil. Proudman noted that peptides, which are building blocks of keratin, are particularly effective. "They bind to the hair shaft as the shampoo or conditioner is rinsed away, which increases the diameter of each strand, creating 'fuller looking' hair," she said. She emphasized, however, that this effect does not involve penetration into hair follicles.
While increased blood flow to the scalp can stimulate hair follicles, Proudman stated that no shampoos currently on the market have been scientifically proven to achieve this. "Unfortunately, the rate of hair growth is inherited and you'll have the same number of follicles that you're born with throughout your life," she added.
Products containing collagen, peptides, and niacinamide (vitamin B3) can make hair strands appear thicker. Ingredients like rosemary oil, tea tree, ginger, and menthol may help soothe the scalp and reduce inflammation, potentially aiding follicle health. Proudman suggests that leave-on treatments like serums are more likely to yield significant results due to their longer contact time with the scalp compared to shampoos.
Products containing caffeine, however, are viewed with skepticism by Proudman. While some studies suggest caffeine can boost blood flow and block hormones that limit hair growth, she noted that most supporting evidence comes from laboratory conditions, not human trials. "There's little proof you'd get the same effect on a human scalp, especially within a shampoo that's quickly rinsed off," she commented, calling it "more marketing than science."
Many marketing claims, such as "20 percent fuller hair," are often based on customer surveys rather than rigorous scientific studies. Proudman pointed out that tests on small groups, like L'Oreal Elvive Growth Booster's trial on 87 people, lack the scientific validity of double-blind, randomized placebo studies, which require a minimum of 12 weeks and baseline measurements for reliable conclusions.
Regarding claims of reversing gray hair, Proudman advised caution. Graying is primarily due to genetics, stress, or environmental factors leading to a loss of pigment. While some products might use colorants to tone down the appearance of gray hair, they do not alter the underlying process. The Cosmetic, Toiletry and Perfumery Association (CTPA) concurs, stating that hair dye remains the only proven method to change the color of gray hair.