It’s not exactly straightforward. “When it comes to hair growth products, many dermatologists (myself included) generally recommend leave-on topical products like a solution, oil, or foam over a shampoo,” says Dr. Kash. “This is because the time in contact with the scalp is limited with a shampoo as it is usually rinsed out after a few seconds or minutes. This limits potential effectiveness compared to a topical leave-on product.” Many of the ingredients found in hair growth shampoo, she adds, were studied as topical leave-on treatments, not in shampoo formulas, so there is little to no evidence they have the same effect in a shampoo.

That being said, there can be be benefit to using a hair growth shampoo. “The wrong shampoo can definitely wreak havoc on the scalp and worsen hair loss,” explains Dr. Kash. For instance, if someone has dandruff, but does not use an appropriate anti-dandruff shampoo, the dandruff can get worse, leading to inflammation on the scalp which can “potentially worsen hair loss.” Conversely, someone with a dry scalp who is using a shampoo with harsh surfactants or detergents can make their scalp dryness even worse, which may also worsen hair loss.

Essentially, it’s about using the right shampoo for your scalp and hair, advises Dr. Kash. “If any shampoos lead to scalp irritation, flaking, redness, itching or increased hair loss, it should be discontinued.”