The appearance of new, thicker hair where there was once only fine fuzz can be a surprising development. Humans have two primary types of hair: vellus hair and terminal hair. Vellus hair is the short, light-colored, thin hair, often called “peach fuzz,” that covers most of the body. Terminal hair is the longer, thicker, and more pigmented hair found on the scalp, eyebrows, and eyelashes. New hair growth occurs when a vellus hair follicle is stimulated, typically by hormones, to transform into a terminal hair follicle, producing a coarser, darker strand. This conversion can be influenced by internal and external factors throughout a person’s life.
Hormonal Shifts Throughout Life
The most common reasons for changes in hair growth patterns are hormonal shifts that occur during major life stages. Androgens, present in everyone, are the primary drivers of this change, causing vellus follicles to convert into terminal ones in sensitive areas. The level of androgen sensitivity in hair follicles is determined by genetics.
Puberty brings the first major surge in androgens, leading to the development of terminal hair in the pubic and axillary (armpit) regions. Hair follicles respond to this new hormonal environment by producing thicker, darker hair.
During pregnancy, elevated estrogen levels prolong the hair cycle’s growth phase. This often increases hair density on the scalp and can sometimes cause new, coarser terminal hair on the abdomen or lower back. Following childbirth, the sharp drop in estrogen levels can trigger increased hair shedding, known as telogen effluvium.
Later in life, perimenopause and menopause introduce another major shift. As estrogen production decreases substantially, the ratio of androgens to estrogens effectively increases. This hormonal imbalance can cause scalp hair follicles to miniaturize and thin, while stimulating terminal hair growth on the face, such as the chin or upper lip.
Prescription and Over-the-Counter Triggers
Certain medications can cause excessive hair growth as a side effect. This condition is known as hypertrichosis, or hirsutism if the growth follows a male-like pattern. This hair growth is a direct response of the hair follicle to the chemical compound, often by interfering with the natural hair cycle or mimicking sex hormones.
A common over-the-counter example is Minoxidil, used to treat scalp hair loss, which can cause localized or generalized hypertrichosis on other body areas. Immunosuppressive drugs, such as Cyclosporine, used to prevent organ rejection, also cause generalized hair growth by stimulating hair follicles.
Other medications associated with increased hair growth include:
- Hormonal therapies like testosterone or dehydroepiandrosterone (DHEA) supplements, which directly increase androgen levels and can induce hirsutism.
- Anti-seizure medications, such as Phenytoin.
- Certain corticosteroids.
If new hair growth begins shortly after starting a new treatment, consulting a healthcare provider to explore alternative medications may resolve the issue.
Underlying Endocrine and Health Disorders
When new, coarse hair growth is rapid, severe, or accompanied by other symptoms, it often signals an underlying endocrine disorder involving the overproduction of androgens. Polycystic Ovary Syndrome (PCOS) is the most frequent cause of hirsutism, affecting up to 10% of women. In PCOS, the ovaries produce excessive androgens, often driven by insulin resistance, which stimulates hair follicles to produce terminal hair in male-pattern areas like the face, chest, and abdomen.
Adrenal gland disorders, though less common, can also be a source of androgen excess. Cushing’s Syndrome, caused by prolonged exposure to high levels of the hormone cortisol, can lead to hirsutism. The excess cortisol can stimulate the adrenal glands to produce more androgens and may also increase the hair follicle’s sensitivity to these hormones.
Another adrenal condition, Congenital Adrenal Hyperplasia (CAH), specifically the late-onset or non-classic form, involves a genetic enzyme deficiency. This deficiency prevents the proper synthesis of cortisol, causing a buildup of hormone precursors shunted toward androgen production. The resulting high androgen levels lead to hirsutism, often starting around puberty. Sudden, severe hirsutism accompanied by symptoms like voice deepening or changes in menstrual cycles should prompt an immediate medical evaluation, as it may indicate a more serious underlying condition or a rare androgen-secreting tumor.
Natural Changes Due to Age and Genetics
Hair growth patterns are significantly influenced by genetic inheritance and ethnic background. Genetic factors largely determine the density, color, and distribution of a person’s hair from birth. For example, individuals of Mediterranean, Middle Eastern, or South Asian descent often have a genetic predisposition for more visible body and facial hair compared to those of East Asian or Native American ancestry.
This variation is partly due to differences in hair follicle size and the sensitivity of those follicles to normal levels of circulating androgens. The hair follicles themselves are present in almost all areas of the body, but genetics dictate which ones are activated to produce terminal hair.
Aging also introduces non-hormonal, inherent changes in hair distribution. As both men and women age, a natural shift occurs where hair growth may slow down overall, but certain areas see an increase in coarse terminal hair. In men, it is common to develop longer, thicker hairs in the ears, nose, and eyebrows later in life. This is a normal part of the aging process, representing a change in the hair follicle’s programmed response over time.