Hair texture changes, often becoming wavier or curlier, frequently coincide with significant hormonal shifts like puberty or hormone therapy. This leads many people to question if testosterone, a powerful sex hormone, directly causes this shift in curl pattern. Understanding the truth requires distinguishing between the hormone’s established role in hair growth and its influence on the hair’s physical structure. This article examines the scientific evidence regarding testosterone’s effects on hair, specifically addressing its ability to induce curliness.
What Determines Hair Texture
Hair texture (straight, wavy, or coiled) is fundamentally determined by the geometry of the hair follicle beneath the scalp. A perfectly round follicle produces straight hair. Conversely, an oval or elliptical follicle causes the hair shaft to bend as it grows, resulting in wavy or curly hair; the flatter the oval, the tighter the curl.
The internal structure of the hair shaft also contributes to texture. Hair is primarily composed of keratin proteins, and the bonding of these proteins dictates the hair’s shape. Permanent chemical structures called disulfide bonds form between keratin molecules. In straight hair, these bonds are distributed evenly, but in curly hair, they are often asymmetrical, creating tension that causes the strand to twist and curve.
How Testosterone Affects Hair Growth
Testosterone, an androgen, plays a well-documented role in regulating the hair growth cycle across the body. The enzyme 5-alpha reductase converts testosterone into Dihydrotestosterone (DHT), a more potent metabolite. DHT is the primary androgen that interacts with hair follicles by binding to specialized androgen receptors.
The effect of DHT depends heavily on the hair’s location. On the face, chest, and pubic area, DHT stimulates growth, converting fine vellus hairs into thicker terminal hairs, especially during puberty. However, in genetically susceptible scalp follicles, DHT is destructive, triggering miniaturization. This process is the underlying cause of androgenic alopecia, or male-pattern baldness.
Miniaturization involves the shrinking of the hair follicle and a drastic shortening of the anagen (active growth) phase. The hair produced becomes progressively finer, shorter, and less pigmented with each cycle. Eventually, these follicles can become dormant, ceasing hair production entirely. This effect relates to hair density and lifespan, not a fundamental change in the hair’s curl pattern.
The Relationship Between Hormones and Curliness
The scientific consensus leans away from a direct cause-and-effect relationship between testosterone and curliness. The primary determinant of curl—the shape of the hair follicle—is established by genetics. While testosterone and DHT affect the hair cycle and follicle size, they do not re-engineer a straight follicle into an oval, curly one.
Changes in texture observed during hormonal flux (such as puberty or hormone replacement therapy) are usually secondary or indirect effects. Shifting hormone levels can alter the hair cycle length and slightly vary follicle size, influencing protein expression. For instance, hair may grow longer, becoming thicker and heavier, which can change how a slight natural wave expresses itself.
When scalp hair appears curlier during hair loss, this is often a deceptive observation. As DHT causes miniaturization, the remaining strands are thinner and weaker. A thin, light strand is more susceptible to kinking or twisting. Furthermore, a slight, previously unseen genetic curl may become noticeable when the strand’s diameter is reduced. The balance of hormones also affects oil production and moisture content, influencing curl definition and frizz.
Other Factors That Change Hair Texture
Hair texture is not fixed and can evolve over time due to several factors unrelated to androgen levels.
Aging
Aging is a significant contributor, as hair follicles naturally change over time. As people age, hair often becomes finer, drier, and may take on a wirier texture due to decreased production of natural scalp oils (sebum).
Health and Environmental Factors
Various health issues and treatments can induce unexpected texture shifts:
- Thyroid disorders frequently lead to changes in hair quality, sometimes causing hair to become coarse and brittle.
- Certain medications, notably chemotherapy drugs, can cause hair to regrow with a completely different texture, often curlier than before.
- Chronic high stress can elevate cortisol levels, disrupting the hair growth cycle and potentially leading to weaker or altered hair strands.
- Nutritional deficiencies (involving protein, iron, or zinc) can compromise the hair’s structural integrity, making it dull, dry, or prone to breakage.