Everyone's Health

Some scars do not tan, Why?

The most obvious possible explanation is that the scar tissue has fewer melanocytes – cells that produce the dark pigment melanin – than the surrounding skin. However, this does not appear to be the case.

In one study, researchers took biopsies from old, pale scars and from the adjacent normal skin of Caucasian volunteers. The researchers were surprised to discover that the number of melanocytes was about the same in scar tissue and nonscar tissue. In addition, the amount of melanin appeared to be similar in the scarred and normal skin.

The researchers proposed two hypotheses to explain why scars may appear pale even though melanocytes are present and appear to be functioning normally. First, there may be fewer blood vessels in scar tissue, resulting in decreased blood flow and whiter skin. Second, the structural properties of scar tissue can cause it to reflect light differently than normal skin.

In normal skin, fibers of the structural protein collagen are randomly oriented. As a result, skin scatters light in random directions. When skin is injured, the interwoven arrangement of collagen is destroyed.

In an effort to repair the damage as quickly as possible, the body lays down new collagen fibers in linear strips oriented parallel to each other. The scar reflects light mainly along a direction perpendicular to the skin.

Also, the upper layer of the skin over the scar may be thinner and may absorb less light. Thus the scar may reflect more light toward the observer and appear whiter.

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