Many men struggle with baldness and wonder about new treatments. Some shampoos and lotions contain caffeine and promise to help keep hair thick and full. How does the evidence stack up?

A 2014 study found that caffeine has a “potent” effect in growing hair in laboratory conditions. But real-world tests of the efficacy of caffeine-containing shampoos and lotions are rare, and those that have been done show a modest effect.

The laboratory work sounds “really promising. But in terms of clinical application we’re not there yet,” says Tina Alster, a clinical professor of dermatology at Georgetown University in Washington, D.C. More rigorously designed studies in humans are needed, she says.

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Androgenetic alopecia, which can affect both men and women, is hair loss caused as testosterone shortens the hair follicle’s growth cycle, resulting in progressively shorter, finer hair, says Ingrid Roseborough, a clinical instructor at the department of dermatology at the University of California, San Francisco.

In the 2014 study published in British Journal of Dermatology, a team of academic researchers found that small concentrations of caffeine, applied to hair follicles extracted from human males and grown in a lab, counteracted the effects of testosterone, stimulating hair growth and prolonging the time the hair follicles remained in their growth phase. The study found the caffeine also had a beneficial effect on female hair growth, but only when used in an even more diluted form than was used for male hair follicles.

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