Despite many women finding Bruce Willis hotter when he lost his hair, baldness is still one of the biggest concerns of men. A number of treatments are available on the market but it can be hard to find the best one that promotes hair growth.

But an effective baldness treatment may not come in the form of a drug or topical cream. Researchers at the University of Wisconsin-Madison developed a wearable technology that works to prevent hair loss. 

Developers said their device is low cost and can be worn underneath the crown of a hat. The wearable tech is powered by the movement of the user, which eliminates the need for a bulky battery.

The device, described in the journal ACS Nano, works by stimulating the skin with low-frequency electric pulses. The energy taps dormant follicles to reactivate and begin hair production. 

Researchers said the wearable tech would work well with men in the early stages of pattern baldness.

“I think this will be a very practical solution to hair regeneration,” Xudong Wang, a professor of materials science and engineering at UW-Madison, said in a statement. “Electric stimulations can help many different body functions.”

When tested on hairless mice, the device stimulated hair growth with low levels of electric pulses. Researchers said it worked as  effective as two different compounds from baldness treatments.

The electric pulses did not penetrate deeper than the outermost layers of the scalp. Users receive only gentle stimulations that will not cause any side effects, the researchers said. 

“It’s a self-activated system, very simple and easy to use,” Wang said. “The energy is very low so it will cause minimal side effects. Before our work there was no really good solution for low-profile devices that provide gentle but effective stimulations.”

Some baldness treatments, like Propecia, are known for causing unwanted effects. The medications have been linked to increased risk of sexual dysfunction, depression and anxiety.

However, the electric stimulation from the wearable tech only switched on dormant hair-producing structures. Wang’s team said the device may not work in men who have been bald “as a billiard ball” for several years.

Hair Device UW-Madison Materials Science and Engineering Professor Xudong Wang (left) and colleagues developed an device — unobtrusive enough to fit under a cap — that harnesses energy from the wearer and delivers gentle electric pulses to stimulate dormant hair follicles and regrow hair. Sam Million-Weaver/UW-Madison