Experiencing an unexpected change in hair texture—whether it is a shift in curl pattern, strand thickness, or overall density—is a common phenomenon. Hair texture is fundamentally determined by the shape of the follicle from which it grows. Any biological or external factor that influences the follicle’s structure or the hair shaft’s integrity can lead to a change. Understanding the root cause of these shifts involves looking at internal biological processes that regulate hair production.
Genetics and the Natural Aging Process
The initial texture of hair is primarily genetic, dictated by the shape of the hair follicle. A perfectly round follicle produces straight hair, while an increasingly oval or flattened follicle shape yields wavy, curly, or coily hair. As a person ages, the hair follicle itself undergoes structural changes that can alter the hair it produces.
The natural aging process, known as senescence, causes the follicle to shrink and its shape to subtly change. This shift can result in previously curly hair growing out looser or straighter, or straight hair developing an unexpected wave or a coarser feel. Furthermore, as the follicle ages, the production of sebum, the natural oil that lubricates the hair shaft, decreases.
Reduced sebum leads to hair that is drier and can feel wirier or more brittle. The loss of melanin, the pigment that gives hair its color, also coincides with an alteration in texture, often making gray or white strands feel thick and rough. Changes in hair density are also a typical part of aging, as follicles spend less time in the growth phase, resulting in finer individual strands and overall thinning.
Hormonal Fluctuations
The endocrine system plays a profound role in regulating the hair growth cycle and is a frequent cause of texture change. Hormones like androgens, estrogen, and thyroid hormones directly influence the shape and function of the hair follicle. Major life events characterized by hormonal surges or declines often correlate with noticeable texture shifts.
Puberty is often the first significant time a person experiences a texture change, as increasing androgen production can cause the hair follicle to morph into a more oval shape, leading to the emergence of curls or waves. Conversely, during pregnancy, elevated estrogen levels can extend the hair’s growth phase, often resulting in thicker, denser hair with enhanced curl definition. This temporary change reverses postpartum when hormone levels drop, leading to shedding and a return to the pre-pregnancy texture.
The decline of estrogen during perimenopause and menopause can lead to a relative dominance of androgens, which can shrink hair follicles and cause strands to grow back thinner. This hormonal shift can cause previously curly hair to straighten out, lose definition, or grow in with a mixed pattern of textures. Beyond sex hormones, thyroid issues are a common culprit; both an overactive (hyperthyroidism) and underactive (hypothyroidism) thyroid can disrupt metabolism and lead to fragile, dry hair, or a complete change in curl pattern.
Systemic Health and Nutritional Deficiencies
The body prioritizes resources for survival, meaning that hair production is often compromised when systemic health is unstable or resources are scarce. Since hair is predominantly composed of the protein keratin, the quality of the hair shaft is dependent on nutrient availability. Deficiencies in specific micronutrients can cause hair to grow out weak, brittle, or significantly finer.
Iron is particularly important because it is needed to produce hemoglobin, which transports oxygen to the hair follicles; a deficiency can prematurely push hair into the resting phase (telogen effluvium), leading to shedding and subsequent texture changes upon regrowth. Vitamin D is also necessary for activating hair follicles, and low levels have been linked to conditions that disrupt the hair cycle. Insufficient protein intake, which is needed to synthesize keratin, can also lead to hair thinning and breakage.
Periods of severe illness or chronic psychological stress elevate cortisol levels, which can trigger telogen effluvium, causing a large amount of hair to enter the shedding phase. When this hair regrows, it may initially have a noticeably different texture or thickness. Certain autoimmune conditions, such as alopecia areata, directly attack the hair follicles, leading to patchy hair loss or the regrowth of hair with a drastically altered, sometimes finer or whiter, texture.
Environmental and Chemical Damage
External factors primarily affect the existing hair shaft rather than the follicle, compromising the hair’s structure and altering its physical appearance. Chemical processes like permanent waving, relaxing, and bleaching deliberately break and reform the hair’s internal disulfide bonds to change texture. Overlapping or improperly executed chemical treatments can severely degrade the hair’s keratin structure, leading to a mushy, stretchy feel when wet and a brittle texture when dry.
Heat styling tools, such as flat irons and curling wands, temporarily change texture by breaking and reforming the hair’s weaker hydrogen bonds. However, temperatures exceeding 350°F (175°C) can cause permanent damage, leading to cracking of the outer cuticle layer and denaturation of the internal keratin proteins. This heat damage results in a rough, crispy texture and a loss of the hair’s natural elasticity, often causing textured hair to lose its curl pattern.
Environmental factors also play a role in short-term texture changes, particularly exposure to humidity. Water molecules in humid air break the hydrogen bonds within the hair fiber, causing hair to revert to its natural shape and resulting in frizz. Additionally, hard water, which contains high concentrations of minerals like calcium and magnesium, can build up on the hair shaft, leaving it stiff, dull, and resistant to styling.