One such ingredient that both she and Dr. Mirmirani recommend is minoxidil, “which is a drug with a long and proven track record for hair growth,” says Dr. Mirmirani. “These minoxidil serums will have a benefit, but are often more costly than over-the-counter minoxidil solution or foam.” (That investment may be worthwhile if a serum makes you more likely to apply it consistently, which typically yields better results.)
Also, consider avoiding formulations that contain additives that might irritating to the scalp and inadvertently cause dryness or itchiness, such as harsh chemicals, dyes, and fragrances. Instead, seek out those that have been dermatologist-tested, says Dr. Shaver.
What’s the difference between a serum and a supplement?
For one, supplements, which are often taken orally, can “address specific nutritional deficiencies that may be lacking in a person’s diet,” says Dr. Mirmirani. So, they can be helpful to address systemic causes of hair thinning, such as a deficiency in certain nutrients. (For instance, research has found that deficiencies in iron, vitamin D, and folate may correlate to hair thinning or slow hair growth.)
But these do take longer to work, as supplements “must first be metabolized by the body and dispersed by the bloodstream to be beneficial,” says Dr. Shaver. And oral supplements may have more systemic side effects and interactions with other medications, so it’s especially important to check with your doctor before taking a supplement.
Meanwhile, “the goal of a serum is to target the hair follicle directly by delivering compounds that may allow for improved or optimal hair growth,” says Dr. Mirmirani. These ingredients are those that aren’t typically found in the diet, such as minoxidil and plant-based compounds.
Topical serums tend to be better for “addressing superficial concerns, such as scaling of the scalp and dryness of the hair shaft, since the product can be applied directly to the location that needs the serum,” says Dr. Shaver, who notes that they can also offer benefits more quickly, such as hydrating and comforting the scalp.
How to apply hair growth serums
The most important step is to test your serum before using it for the first time. “Apply the serum to a small spot on the scalp for a few days to ensure that there is no irritation before applying it more broadly,” says Dr. Mirmirani. “A measured approach is best.” To that end, get comfortable with the fact that you’ll need to be both consistent and patient in your usage, as the results can take time.
As for the application itself, apply a hair growth serum to a clean scalp (though this might vary with the exact product). Ideally, it helps to do it while hair is lightly damp, since this “can help to disperse the product across the scalp and make the scalp more porous and enhance absorption,” says Dr. Shaver. (However, she notes, a very wet scalp would dilute your serum and potentially make it less effective.)