Scarring alopecia

Scarring alopecia is permanent hair loss caused by destruction of hair follicles and their replacement by scar tissue. It includes inflammatory disorders that damage follicles and prevent regrowth.

Hair follicle: A skin structure that produces hair through a cycle of growth, regression, and rest. Scarring alopecia permanently removes this structure rather than merely interrupting its growth cycle.
Lichen planopilaris: A lymphocytic scarring alopecia that commonly causes patchy hair loss on the scalp. It is a major inflammatory form of scarring alopecia.
Androgenetic alopecia: A patterned form of hair loss caused by progressive follicle miniaturization and genetic sensitivity to androgens. Its follicles shrink rather than being replaced by scar tissue.
Trichoscopy: A magnified examination of scalp and hair using a dermatoscope. It can show absent follicular openings and inflammatory clues that support diagnosis.
Peroxisome proliferator-activated receptor gamma: A nuclear receptor that regulates gene expression involved in metabolism, inflammation, and cell differentiation. Its disruption has been investigated as a contributor to follicular inflammation and scarring.
Lymphocytic scarring alopecia: A group of scarring alopecias in which lymphocytes are the predominant inflammatory cells. These disorders damage follicles through lymphocyte-centered inflammation.
Frontal fibrosing alopecia: A scarring alopecia marked by progressive recession of the frontal and temporal hairline. This recognizable pattern is a clinical variant of lichen planopilaris.
Alopecia areata: An autoimmune disorder that causes nonscarring, usually patchy hair loss. Hair may regrow because follicles are not permanently destroyed.
Scalp biopsy in alopecia: Microscopic examination of a scalp tissue sample to classify hair-loss disorders. Biopsy location and tissue processing help distinguish scarring subtypes.
Cutaneous microbiome: The community of microorganisms living on the skin and its surface. Its role in triggering or sustaining particular scarring alopecias remains under study.

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