Coffee could hold the secret to curing male baldness, according to new research.
The finding could lead to new treatments for a condition that affects half of all British men by the age of 50.
A recent survey of five European countries found that British men are unhappier about being bald than most of their European counterparts, but are too embarrassed to do anything about it. More than half said going bald made them feel old and less attractive.
The new study, published in the International Journal of Dermatology, found that caffeine works by blocking the effects of a chemical known to damage hair follicles.
But drinking plenty of coffee may not be the best answer.
Scientists estimate up to 60 cups a day would be needed for significant amounts to reach follicles in the scalp.
Instead, German cosmetics firm Alpecin has developed a caffeine-rich solution that can be rubbed on the scalp.
"Caffeine is a well-known substance, yet little is known about its effect on human hair follicle growth," said Dr Tobias Fischer, who carried out the latest research at the University of Jena in Germany.
"But this study shows it's a promising candidate for hair growth stimulation."
Most baldness is caused when hair follicles, the tiny sacs in the scalp from which hair grows, become exposed to too much dihydrotestosterone, or DHT. This is a chemical produced by the male hormone testosterone.
The follicles shrink if there is too much DHT circulating in the blood, so the hair becomes thinner and grows for less time than normal.
Experts believe men with high levels of testosterone are more likely to lose their hair, especially if baldness already runs in the family.
Many men try over-the-counter scalp lotions to boost hair growth, but these are mostly unproven.
In recent years, anti-baldness drugs have been developed. They work by stopping DHT from reaching the follicles and stunting growth.
But they are not available on the NHS and have to be taken for up to two years before they have an effect.
Some men resort to hair transplants, taken from the back or sides of their heads on to the top to cover the receding patches.
But this relies on transferring individual hair follicles rather than millions of active cells.
British company Intercytex is developing a technique involving taking a tiny sample of skin from the head and using it to mass produce dermal papilla - the cells which have already matured into hair-growing factories.
These are then injected back into the scalp, potentially giving a full head of hair.
Despite these advances, a caffeine-based lotion could be a cheaper and equally effective alternative to baldness.
To test the idea, Dr Fischer took scalp biopsies from 14 men in the early stages of hair loss.
He extracted hair follicles and placed them in test tubes with solutions containing different levels of caffeine.
The samples were left in the laboratory for up to eight days to monitor growth. At the end of the experiment, caffeine had boosted the length of the hairs by between 33 per cent and 40 per cent.
In contrast, other test tubes containing hair follicles mixed with testosterone showed that they grew much more slowly.
Scientists behind the breakthrough believe caffeine affects hair cells in such a way that they are able to resist the damaging effects of DHT.
"Hair follicles that were treated with caffeine showed a highly significant growth rate at 24 hours, and still showed further significant growth at eight days," said Dr Fischer.