T cells are white blood cells that play a central role in the human immune system. Researchers at Georgetown University found that blue light makes T cells move faster. Human skin stores twice the number of T cells than is circulating in the blood.

“T cells need to move to the site of an infection,” said senior investigator Gerard Ahern. “We know that blue light can reach the dermis, the second layer of the skin, and that those T cells can then move throughout the body.” Ahern said there is more work to do to understand the findings but it might make sense to offer patients blue light therapy to boost their immunity.

Source: https://medicalxpress.com/news/2016-12-sunlight-benefitit-energizes-infection-cells.html