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Menopause Matters

Postmenopausal Hair Growth Patterns

Ruth Freeman, MD

Changing patterns of hair growth are a problem for many postmenopausal women, although the effect of menopause on these changes has not been well studied.

There are three types of human body hair: lanugo, vellus, and terminal. Lanugo hair is seen mostly in newborns, and is usually shed within a few months of birth. Vellus hair is soft and fine, and is only a few millimeters long. It is present on most areas of the body, although it is not very noticeable. Terminal hair is the thick, dark hair on the scalp and eyebrows, as well as the androgen-induced hair on the face, chest, and axillary and pubic areas.

During childhood and early adulthood, more than 50 million hair follicles are present on the body, with 100,000 to 150,000 in the scalp. At about age 40 years, the number of hair follicles begins to decline as a result of aging.

Terminal hairs on the scalp and eyebrows are present throughout life. However, growth of this type of hair on other areas of the body (eg, face, axillary and pubic areas, abdomen, chest) depends on exposure to the androgens dehydroepiandrosterone and testosterone, which are converted to dihydrotestosterone by the enzyme 5α-reductase. Dihydrotestosterone is the primary agent that acts on the hair follicle, causing growth of body hair and loss of scalp hair.1-3

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PHASES OF HAIR GROWTH

Hair undergoes three phases of growth: anagen, catagen, and telogen. Anagen is the active growing phase; catagen is the phase during which the hair shaft involutes; and telogen is the resting phase, after which the hair falls out (pushed out by the new anagen hair growing in from below). The duration of each phase varies by body site. The anagen phase in the scalp may last 2 to 4 years, whereas in other areas of the body it only lasts 2 to 3 months. The duration of the other phases remains constant in all areas of the body. The catagen phase lasts about 2 to 3 weeks, whereas the telogen phase lasts 3 to 4 months.

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FACTORS AFFECTING HAIR GROWTH

A number of cytokines and hormones affect the length of the hair growth phases, as well as the rate of growth. Thyroid hormone deficiency changes the ratio of anagen to telogen hair, resulting in poor growth and loss of hair. Replacement of thyroid hormone corrects this condition, and new hair grows within a few months of treatment. Growth hormone affects this rate as well, in addition to the number of hairs growing at one time.

Androgens have the greatest effect on hair growth. On specific areas of the body, androgens turn vellus hairs into thick, dark terminal hairs. They also lengthen the anagen phase, resulting in longer hair. The mechanism of action is unclear, but it may depend on a particular hair follicleês level of 5α-reductase content or the concentration of androgen receptors.1 In genetically susceptible women, androgens act on scalp hair, shortening the anagen phase progressively until no hair is visible on the skin surface; this is the cause of most baldness in postmenopausal women.

Endogenous estrogen may prolong the hair growth phase, especially on the scalp. This may not be a direct effect, but rather a result of alterations in the concentration of 5α-reductase. When women reach menopause and their estrogen production decreases, loss of scalp hair begins to accelerate. This is due to a combination of the shorter anagen phase, as the hair follicle is exposed to a more androgenic milieu (in genetically susceptible individuals), and to the age-related reduction in numbers of hair follicles.

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ALOPECIA AND HIRSUTISM

Some women in midlife experience thinning of hair on the scalp (androgenic alopecia) and/or unwanted growth of facial hair (hirsutism). Excessive hair growth occurs in 4% to 10% of young, premenopausal women, often in association with menstrual abnormalities,4-6 but the prevalence of abnormal hair growth in postmenopausal women has not been well documented.

The author's research group recently documented hair growth patterns in a large population of postmenopausal US women aged 50 to 79 years who participated in the Womenês Health Initiative (unpublished data, 2006). A total of 656 women were interviewed. Of those, 32.6% were aged 50 to 59 years, 53.7% were aged 60 to 69 years, and 58.2% were aged 70 to 79 years. Seven women were aged 80 years, but no data are presented for them. The study population consisted of white (56.7%), black (29.7%), and Hispanic (12.8%) women.

Alopecia was present in 38.1% of women aged 50 to 59 years, 49.3% of those aged 60 to 69 years, and 68.4% of those aged 70 to 79 years. Excessive facial hair growth after menopause was reported by 32.6% of the 50-to-59 age group, 53.7% of the 60-to-69 age group, and 58.2% of the 70-to-79 age group. Excessive hair growth was largely confined to the face; <1% reported increased postmenopausal hair on the abdomen, chest, or extremities. Some women who had excessive premenopausal hair growth reported an exacerbation of the problem postmenopausally.

No significant differences were found between black and white women regarding either hair loss or excessive hair growth, although growth appeared to be slightly higher among black women. Overall, 27% of the women had both scalp hair loss and excessive facial hair growth. The Hispanic group was too small to compare their data, although the patterns of hair changes appear to be similar.

With rare exceptions, all subjects described loss of pubic, axillary, and leg hair—an observation that has been documented previously.6 These terminal hairs are thought to be androgen dependent, as is facial hair. It has not been explained why androgen-dependent hair grows in some areas while it disappears in other areas.

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CONCLUSION

Both progressive loss of scalp hair and progressive growth of excessive facial hair appear to be associated with both age and the number of years past menopause. The actual causes of hair changes in postmenopausal women remain unknown.

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Ruth Freeman, MD, is professor, Departments of Medicine and Obstetrics and Gynecology and Womenês Health, Albert Einstein College of Medicine and Montefiore Medical Center, New York, NY.

References

1. Courtois M, Loussouarn G, Hourseau C, Grollier JF. Ageing and hair cycles. Br J Dermatol. 1995;132(1):86-93.
2. Olsen EA, ed. Disorders of Hair Growth: Diagnosis and Treatment. 2nd ed. New York, NY: McGraw-Hill; 2003.
3. Azziz R, Carmina E, Sawaya ME. Idiopathic hirsutism. Endocr Rev. 2000;21(4):347-362.
4. Derksen J, Moolenaar AJ, Van Seters AP, Kock DF. Semiquantitative assessment of hirsutism in Dutch women. Br J Dermatol. 1993;128(3):259-263.
5. Venning VA, Dawber RP. Patterned androgenic alopecia in women. J Am Acad Dermatol. 1988;18(5 pt 1): 1073-1077.
6. Ferriman D, Gallwey JD. Clinical assessment of body hair growth in women. J Clin Endocrinol Metab. 1961;21:1440-1447

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