Several research teams are working to figure out ways to spur existing follicles—the tiny organs in the skin that give birth to hair—back into action, or to make new, active follicles. New treatments based on this work likely are many years from the market, but these approaches could lead to the significant breakthrough of helping people who are already bald. By contrast, topical products available now, such as Rogaine, appear to be most effective in helping prevent further balding after it has started. And with current surgical procedures, healthy hairs can be moved into bald areas, but the operation has to be continually repeated.

Crucial to the hair-growth and balding process, scientists have found, are vitamin D and the microscopic receptors that bind to it in skin. These elements have become the focus for several research teams. (Supplements might offer health benefits for people lacking enough vitamin D, but they won’t bring back lost hair, researchers say.)

Some researchers, including those from the San Francisco Veterans Affairs Medical Center and Harvard Medical School, have identified molecules besides vitamin D that appear to activate the receptor and hold potential for future treatments. In July, Japanese researchers demonstrated in animals that adding vitamin D helped the process of using stem cells to generate new follicles.