What's special about red light in promoting hair growth?

This perfect rainbow reminds us all that light is made up of many different wavelengths ranging from 400 nm to 700. Wavelengths around 650 nm produce red light.

Like many things in medicine, the use red light for hair growth came by chance. In the late 1960s, Dr Endre Mester, a Hungarian physician was studying whether a 694 nm ruby laser would cause cancer in mice. To his surprise, the laser did not cause cancer but rather dramatically stimulated hair growth!

It remains unclear exactly how red light stimulates hair growth. It appears that red light stimulates tiny organelles inside cells called mitochondria. A specific molecule known as cytochrome C oxidase (which is part of the mitochondria's cellular respiratory chain) has been proposed to be a key receptor molecule to absorb the red light and start the entire process.

To date, there have been 5 randomized double blind controlled trials studying the use of red light low level laser treatment (at 655 nm) for individuals with androgenetic alopecia. These include 2 studies with a laser "comb" device and 3 with a laser "helmet/cap" device. All studies showed improvement by 16-26 weeks compared to a placebo (sham) device.

There are many unanswered questions about using low level laser therapy. Which device is best? Is 655 nm really the best wavelength? Is the current 3 times per week really the best? Are laser combs better than laser helmets or are helmets better than combs? These are all unknown at present.