Scalp Hair Characteristics in the Newborn Infant

Susan A. Furdon, RNC, MS, NNP; David A. Clark, MD

Disclosures

Adv Neonatal Care. 2003;3(6) 

In This Article

Hair Characteristics

The follicles on the scalp initially produce vellus hair, a silky hair that is seen in full-term infants. Vellus hair is short, fine, and poorly pigmented. Over time, the follicle diameter enlarges, and the hair acquires a myelin sheath. Intermediate scalp hair develops 3 to 7 months after birth and is replaced with mature, thick terminal hair by 2 years of age.[7] Although vellus hair continues to develop and accounts for 6% to 25% of scalp hair, it is less noticeable because of its light pigmentation.[4]

Melanin is responsible for hair pigmentation. Skin melanocytes originate from neural crest cells and migrate to the developing epidermis between weeks 6 and 7 of gestation. Melanocytes in the hair bulb contain subcellular organelles known as melanosomes that synthesize and store melanin. Melanocytes deliver the melanosomes to keratinocytes, where they are incorporated into the growing hair shaft, imparting color to the hair. Different hair colors result from the relative amount and type of melanin.[1,5] Two types of melanin account for all possible hair colors:

  • Eumelanin: colors hair brown to black

  • Pheomelanin: an iron-rich pigment that colors hair yellow-blonde to red

The intensity of hair color depends on the density of pigment within the melanosome. Both eumelanin and pheomelanin are made from the amino acid tyrosine, using the enzyme tyrosinase. Increased tyrosinase activity increases pigment production and results in a darker hair color. Reduced pigment or patchy deposition of pigment within melanosomes results in lighter hair.

Hair color usually follows the tendency of skin color; however, exceptions occur.[8] When comparing hair color with a parent, it is important to note that hair color may change during puberty because of an increase in melanocyte pigment in response to increased hormonal levels. Tyrosinase also is more active with age.[11]

Hair length is fairly uniform over the scalp for any individual infant, but varies significantly between infants. Hair length is related to length of time the hair is in the anagen phase and is unique to a specific body area. Scalp hair will grow long, whereas arm hair only grows 1 to 2 cm.[9] The strength of the hair shaft is related to the elements of protein.[1]

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