Thinning hair is often a result of the aging process, and it affects both men and women in their later decades, usually around age 60, according to Vera Price, M.D., F.R.C.P.C., professor of dermatology, University of California, San Francisco.
"It may start in some individuals before that age, in their 50s, and in others, it may be after that, in their 70s or later," Dr. Price says. "Some individuals do not have it."
Patients typically notice less hair on top of their heads when they experience age-related hair thinning, but increased shedding is usually not associated with this, Dr. Price says.
Age-related hair thinning is not just a continuation of androgenetic alopecia, according to Dr. Price. Some men and women who have age-related thinning may have developed androgenetic alopecia earlier in life, in their 20s, 30s or 40s, she says.
"Androgenetic alopecia and age-related thinning are due to different mechanisms," Dr. Price says. "Androgenetic alopecia is caused by an enzyme, 5-alpha reductase, that converts the male hormone testosterone to a more potent male hormone, dihydrotestosterone, in genetically-prone men and women."
Age-related thinning is not male hormone-driven; rather, it is part of the aging process, which is not well understood.
"We do know that in our later decades, the amount of the enzyme 5-alpha reductase is greatly decreased in the scalp, and age-related thinning also involves a genetic predilection," she says.
Many dermatologists do not recognize age-related thinning as a distinct entity from androgenetic alopecia. This is because biopsies from the two conditions look similar, Dr. Price says. In both conditions, the follicle becomes smaller and smaller, the oil glands remain large, and there is no scarring. In other words, the two conditions cannot be distinguished under the microscope.
Dr. Price says the reason to differentiate the two conditions is for proper treatment selection. Since age-related hair thinning is not driven by male hormones, "Finasteride will not be effective," Dr. Price says.
Age-related thinning will respond to minoxidil, which currently is the only treatment available for the condition. Younger patients with androgenetic alopecia have the option of using minoxidil, finasteride or both, Dr. Price says.
It is important to be sure that there are no other causes involved other than age when patients present with hair thinning.
"I like to check certain laboratory tests to be sure we are not dealing with any other cause of hair thinning other than age," Dr. Price says. "I check the blood count, thyroid-stimulating hormone, ferritin and vitamin [25(OH)] D."
In addition, a clinician should determine the medications that a patient has been taking, as well as whether a patient has recently experienced an acute illness or a high fever.