BSIP, JACOPIN / SCIENCE PHOTO LIBRARY BSIP, JACOPIN / SCIENCE PHOTO LIBRARY
Acne. Artwork showing the formation of an acne spot. A hair shaft and its associated sebaceous gland (pale yellow) are seen in the skin. The sebaceous gland produces sebum, an oily substance which waterproofs the hair (seen at left). These glands are especially active during adolescence. If the hair shaft becomes blocked (centre), the sebum builds up in the shaft, leading to a spot, or whitehead (right).
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