For a healthy head of hair, activate your macrophages. Besides their role in host defense, these immune cells also promote hair growth, according to a report on page 903 by Osaka et al.

New and rapid hair growth is a byproduct of the wound response in mice. The team now finds that this hair growth requires a wound-activated protein kinase called ASK1.

ASK1 was necessary for the up-regulation of a number of immune response factors in wounded skin, including many that are expressed in macrophages. The team found that macrophage recruitment to the wound site and macrophage activation were both significantly reduced in mice lacking ASK1. Transplantation of activated macrophages into the skin of ASK1-lacking mice promoted hair growth even in the absence of wounding.

Although wounding is not necessarily linked to the induction of hair growth in humans, one of the common treatments for alopecia does activate macrophages. The team is currently attempting to purify hair growth–promoting factors that are produced from activated macrophages in the hope of designing more effective drugs to treat alopecia.

Until then, the authors do not recommend a head injury as a home remedy.