Hair texture can change dramatically over a lifetime, often shifting from straight to wavy or curly. This change is rooted in the biology of the hair follicle and is influenced by internal bodily changes. The hair you had as a child may evolve into a completely different texture as you move through various life stages. This transformation reflects underlying physiological processes that alter how hair grows.
The Biology of Hair Shape
The natural shape of an individual hair strand is determined by the form of its hair follicle, a tiny organ extending into the skin. A perfectly round follicle produces straight hair because the hair shaft grows symmetrically. Conversely, an oval or asymmetrical follicle causes the hair shaft to bend as it grows, resulting in wavy or curly hair; the flatter the oval, the curlier the hair will be.
The protein keratin forms the structural bulk of the hair, and its distribution within the hair’s cortex influences the curl pattern. Within the keratin structure are strong chemical connections called disulfide bonds. These bonds form between sulfur atoms in the amino acid cysteine.
In straight hair, the disulfide bonds are more evenly aligned along the shaft. In wavy or curly hair, the asymmetrical follicle shape forces the keratin to cluster on one side, allowing for an uneven distribution and greater number of disulfide bonds. This uneven bonding structure creates the internal tension that results in a curl or wave.
Primary Drivers of Texture Change (Hormonal Shifts)
The most significant biological factor driving hair texture change is the fluctuation of hormones throughout life. Hormones like androgens and estrogens directly affect the shape and function of the hair follicle. These shifts can alter the protein structure and the angle at which the follicle is embedded in the scalp, leading to a permanent or semi-permanent texture change.
During puberty, the surge of sex hormones can activate genes related to hair curl. An increase in androgens can cause hair follicles to become more oval-shaped. This change is why many individuals experience their straight hair developing a noticeable wave or curl pattern for the first time during adolescence.
Pregnancy involves dramatic hormonal change, with high levels of estrogen prolonging the hair’s growth phase. The rapid drop in hormones postpartum can trigger temporary hair shedding known as telogen effluvium. The hair that regrows sometimes emerges with a different texture, such as a new wave pattern. Up to 50% of women report major hair changes during or after pregnancy.
Later in life, the onset of perimenopause and menopause, characterized by a significant decrease in estrogen, can alter hair texture. The relative increase in androgen activity as estrogen declines can cause the hair follicle to shrink and change shape. This may lead to the development of new waves or curls, or cause hair to become finer and drier due to decreased sebum production.
Other Physiological and Environmental Factors
Beyond major hormonal life stages, other physiological processes and external factors can impact hair texture. The overall aging process naturally affects the hair follicle, separate from menopausal hormonal changes. As the body ages, cellular processes slow down, and the hair follicle may begin to produce a thinner, finer hair strand.
Medications
Certain medications are known to cause texture changes as a side effect. Chemotherapy drugs often destroy rapidly dividing cells, and the hair that regrows frequently emerges with a completely different texture, often curlier than before treatment. Medications that affect hormone levels (like certain thyroid drugs) or interfere with cell division (like some anti-epileptics and retinoids) have also been linked to texture changes.
Stress and Illness
Severe illness or periods of extreme physical or emotional stress can trigger telogen effluvium, where a large number of hairs prematurely enter the resting phase. When these hairs regrow months later, the new strands may have a temporarily altered texture due to the disruption in the follicle’s cycle. The hair may feel coarser or more straw-like before it eventually returns to its pre-stress state.
Duration and Permanence of the Change
The duration of a hair texture change depends directly on its underlying cause. Changes driven by genetics or aging, such as those that occur during puberty, are generally permanent because the structure of the hair follicle itself has been permanently altered. The new texture will persist in the hair that grows from the scalp.
Changes linked to temporary physiological events, like pregnancy or short-term medication use, are often temporary, though they may take time to resolve. For example, texture changes following chemotherapy may last for several hair growth cycles before the original texture returns.
If a texture change is sudden, severe, or accompanied by other symptoms like excessive hair loss, unexplained weight changes, or chronic fatigue, consult a healthcare professional. These symptoms may point to an underlying medical condition, such as a thyroid disorder or a nutritional deficiency, that needs to be addressed.