The phenomenon of a baby’s beautiful, tight ringlets disappearing is a common and often surprising observation for new parents. The soft, wispy curls present during infancy frequently give way to a completely different texture, which may be wavy, straight, or even curlier than before. This change is not random, but rather the result of biological shifts occurring beneath the skin as the child grows. The initial hair is temporary, and its replacement is guided by human anatomy, hormones, and inherited traits.
The Anatomy of a Curl
The texture of any person’s hair, from straight to tightly coiled, is determined by the shape of the hair follicle. This follicle is a tunnel-like structure in the outer layer of the skin, and its form acts as a mold for the hair strand it produces. A perfectly round hair follicle generates straight hair, much like extruding dough through a circular opening creates a straight noodle.
Curly hair originates from an oval or asymmetrical follicle, which causes the hair shaft to grow with a natural bend. This shape also leads to an uneven distribution of the protein keratin within the hair strand’s structure. This asymmetrical protein buildup creates tension and causes the strand to spiral. The more oval the follicle is, the tighter the resulting curl pattern will be.
Hormonal and Physical Changes That Alter Follicle Shape
The initial hair a baby is born with, or the fine hair that quickly replaces it, is called vellus hair. Vellus hair is typically short, soft, and lightly pigmented, and its fragility contributes to the loose curls often seen in infants. This fine hair must be replaced by terminal hair, which is the thicker, longer, and more pigmented hair found on the scalp of older children and adults. This transition process is one of the primary reasons the texture changes.
A major trigger for the initial loss of baby hair is the stabilization of hormones following birth. The high levels of maternal hormones circulating in the infant’s system during pregnancy drop sharply after delivery, which signals many hair follicles to enter a resting phase and shed. The new hair that grows in is the first crop of the genetically programmed terminal hair. Simultaneously, the physical growth of the infant’s skull and facial structure subtly changes the angle at which the hair follicles emerge from the scalp. This alteration in the follicle’s angle, combined with its development into its adult shape, molds the new terminal hair into its permanent texture.
Genetics and the Timeline of Hair Transition
The final hair texture is determined by a person’s polygenic inheritance, meaning multiple genes interact to produce the outcome. While a baby may have temporary curls, the hair that replaces the vellus hair reflects their true genetic makeup. The transition from the soft baby hair to this genetically determined adult texture unfolds over the first few years of life.
The most noticeable texture changes typically occur between six months and two years of age as the terminal hair fully takes over. By the age of two, the hair texture is often considered “locked in,” as the follicles have largely matured into their permanent shape. A haircut does not cause the loss of curls; it is merely a coincidence that the texture changes around the time of the first cut. The new hair growing from the root defines the long-term texture, and this biological event replaces the initial baby curls.