A baby’s hair development is a continuous process that begins many months before birth. This journey of hair growth, shedding, and replacement is guided by genetics and hormonal shifts, resulting in significant changes to a child’s hair during their first few years of life. Understanding this process helps parents appreciate the normal variations in infant hair development.
Hair Development Before Birth: The Role of Lanugo
Hair follicles, the tiny structures from which hair grows, begin to form around the 14th week of pregnancy. This establishes a pattern that remains for life, as babies are born with all the hair follicles they will ever have.
Around 16 to 20 weeks of gestation, a fine hair called lanugo emerges, covering most of the fetus’s body. This covering helps anchor the vernix caseosa, a waxy substance, to the skin. Together, the vernix and lanugo protect the delicate fetal skin from amniotic fluid and aid in temperature regulation.
Lanugo is shed into the amniotic fluid between 32 and 36 weeks of pregnancy, where it is swallowed and becomes part of the first stool, called meconium. While most babies are born without it, about 30% of full-term newborns may still have some lanugo. This hair disappears within the first few weeks or months after birth and is usually replaced by vellus hair, often described as “peach fuzz.”
The Post-Natal Transition: Shedding and New Growth
After birth, the initial hair begins to shed. This mass shedding is triggered by a sudden drop in maternal hormones that supported the hair growth cycle during pregnancy. The hair follicles enter a prolonged resting phase called telogen, leading to temporary, widespread hair loss known as telogen effluvium.
Shedding starts around the second month of life and can continue until the baby is about six months old, often peaking at three months. The loss can be significant, sometimes leaving infants who were born with a full head of hair nearly bald.
The hair that replaces the shed newborn hair may differ in texture and color. New growth usually begins between 6 and 12 months, marking the start of more mature hair development. This new hair will be either vellus hair or the thicker, more pigmented terminal hair, and it is often lighter or darker than the original hair.
Understanding Common Hair Changes and Variations
Beyond hormonal shedding, temporary hair loss can result from friction. Many infants develop a bald spot on the back or sides of the head, known as friction alopecia. This is caused by constant rubbing against firm surfaces like crib mattresses or car seats, as babies spend much time lying on their backs.
This friction-induced bald spot resolves once the baby begins to sit up independently and spends less time lying down. Hair color and texture continue to change over the first two years before stabilizing. This is due to evolving genetics, the enlarging shape of the hair follicles, and the gradual accumulation of the pigment melanin in the hair shaft.
Around age two, the finer vellus scalp hair is often replaced by terminal hair, which is thicker and longer. The timing varies widely; one baby may have a full head of hair by their first birthday, while another is still growing in their first set of strands, and both are typical. If a baby older than six months experiences significant hair loss without regrowth, consult a pediatrician.