Skin and hair color

Skin color differences are not clearly visible in premature infants until around 32 weeks gestation.⁸ Although melanocytes are active at birth, pigmentation is not fully developed in newborns, especially those with darker complexions. Their skin tone will deepen gradually over the first several months of life.⁹ This postnatal darkening is partly due to increased melanin production triggered by exposure to ultraviolet (UV) light after birth.¹⁰

Fetal hair development follows a predictable timeline, beginning early in gestation and continuing through several distinct stages before and after birth. Hair follicles begin forming on the face around 14 weeks of gestation, gradually maturing into fully developed follicles by about 20 weeks.¹¹ Interestingly, hair development on the lower body starts around 19 weeks gestation, more than a month after the face.¹²

The first hairs that grow around 14 weeks gestation are soft, fine strands called lanugo. Lanugo becomes plentiful by 19 weeks gestation and helps hold the vernix caseosa on the skin.¹³ These early hairs start in a growing phase. However, around the fifth month of pregnancy, these hairs shift into a resting phase over the course of about a week to 10 days.¹⁴ Many of the earliest lanugo hairs are shed between 8 and 9 months of pregnancy and get replaced by vellus hair—short, thin strands like peach fuzz.¹⁵ Although a baby is born with a full set of hair follicles on her head, the type of hair she has at birth will change. Eventually, vellus hair on the head is replaced by the longer hair typical of older children and adults called terminal hair.¹⁶ At birth, the body has about 5 million hair follicles, and while no new ones form after birth, each strand grows thicker and larger with age.¹⁷

A baby’s permanent hair color is predetermined by the chromosomes that she received from her mom and dad. Her genetics orchestrate the location and production of a natural pigment called melanin. Hair color is determined by the type and amount of melanin produced by cells called melanocytes. These cells gradually migrate into the hair follicles, into a part called the hair bulb, where they begin producing melanin.¹⁹

There are two main types of melanin:

• Eumelanin, which gives hair black or brown tones. 
• Pheomelanin, which produces red or yellow tones.

The mix and concentration of these two types of melanin determine the baby’s hair color.²⁰

By the second trimester, melanocytes are active in the hair follicles and begin transferring melanin into the cells that form the hair shaft. However, hair is still developing, so the color may not be fully visible yet. Melanin production increases as the fetus grows, and hair begins to emerge with pigment in the third trimester.²¹

Importantly, melanin production may continue to change after birth. In a study of white European children, many infants were observed to have darker hair during the first six months of life. Between 9 months and 2½ years of age, their hair lightened noticeably. After age 3, however, their hair gradually darkened again, continuing this trend until around age 5.²² In short: a baby’s hair color starts forming in the womb, but it may change over the first months or even years of life as melanin levels stabilize.