Understanding the biology of hair loss may do more than just satisfy people's vanity -- it may help people who are sick.
Studying the signals that drive hair growth gives insights into what causes cancer, why the immune system sometimes attacks its own body, and how specialized cells and organs develop. If these efforts bear fruit, understanding hair may go well beyond a cure for baldness.
* Cancer: Each hair follicle contains a set of adult stem cells that divide very rapidly to regenerate the follicle each time it passes into a new growth phase. Those stem cells, scientists have learned, are more likely than other skin cells to form cancers.
Elaine Fuchs, a professor at Rockefeller University, is studying the proteins that tell hair follicles to grow or stop growing. She found that mice with abnormal versions of a protein called beta-catenin grew new hair follicles as adults, even though follicles normally develop only in embryos. As the protein kept telling the follicles to grow, the cells kept dividing and ultimately turned into tumors.
Fuchs' lab has since shown that a common type of human skin cancer comes from follicles that have trouble destroying beta-catenin.
Her findings might lead to drugs to help bald people grow more hair -- or to slow the progress of skin cancer.
* Immune system: Usually, the body is wary of cells that divide very rapidly, like those in hair follicles: After all, they might be cancerous. But hair is special. Follicles are "immune privileged," meaning that the immune system does not go after them, even if they're transplanted.
The breakdown of this immune privilege leads to a common condition called alopecia areata that can cause anything from hair loss in a small patch to complete loss of hair.
Like other autoimmune diseases such as lupus, alopecia areata happens when the body becomes confused about what is part of it and what is a foreign invader. The immune system attacks the hair follicles as if they were germs, preventing the hairs from growing.
About 5 million Americans have the condition, which usually starts in childhood. What triggers it is unknown -- but as scientists begin to understand, they may be able to cure not only alopecia areata but also develop treatments for other, much more serious autoimmune diseases, or prevent rejection of transplanted organs.
* Differentiation: The adult stem cells that serve as a reservoir to regenerate the follicle can do much more than that, at least in the laboratory. Scientists have reported that they can become a variety of other types of cells.
"Hair follicle cells can become nerve cells; they can become bone," says Angela M. Christiano, a dermatology professor at Columbia University.
Studying the signals that cause hair follicle cells to become one cell type over another will help cell biologists understand the fundamental principles of cell growth, division and differentiation.
Hair scientist Colin Jahoda, a professor at Durham University in England, has found that follicle cells can also become blood cells, at least in mice.
His work is encouraging for leukemia patients, who often need difficult and painful transplants of bone marrow cells, which generate the blood cells. Hair follicles might be able to provide a much more accessible source of blood cells for these patients.