Discoloration

Discoloration is a change in color that departs from the normal appearance of an object or tissue. It can affect natural materials such as textiles or metals, or living tissues such as skin, teeth, and nails. Discoloration may be intrinsic, arising from composition or structure, or extrinsic, produced by external agents such as stains, contamination, or environmental exposure. It is a common concern in manufacturing, conservation, and medicine, and can provide diagnostic clues or indicate quality issues.

Causes and mechanisms differ by domain. In materials, oxidation, corrosion, heat, chemical reactions, and UV exposure can alter color. In biology, pigments (melanin, hemoglobin, bilirubin), changes in blood flow, or tissue damage can produce color changes. External sources include dyes, mineral deposits, mold, or surface contamination.

Typical forms include skin discoloration (hyperpigmentation, hypopigmentation, cyanosis, pallor, jaundice), bruising, and tooth staining. In metals and stones, rust and mineral staining can change appearance. In textiles, dye transfer, fading, or staining from liquids are common causes.

Diagnosis relies on visual inspection and history, with targeted tests as needed (for example, laboratory tests for liver disease in jaundice, or spectroscopic analysis for materials).

Management focuses on addressing the cause and, when appropriate, restoring appearance. Treatments include removing stains, protective coatings or sealants for materials; cosmetic whitening or laser therapy for skin discoloration; medical treatment for underlying diseases; and preventive measures such as sun protection, proper storage, and regular cleaning.