A wrinkle is a ridge or crease of a surface. It usually refers to folds on fabric or clothes, or on the skin of an organism; the folds are generally random and do not exhibit any repeating pattern. In skin or other foldable material a wrinkle or fold may be permanent if the material is folded the same way each time.
Skin wrinkles typically appear as a result of aging processes such as glycation or, temporarily, as the result of prolonged (more than a few minutes) immersion in water. Wrinkling in skin is caused by habitual facial expressions, aging, sun damage, smoking, poor hydration, and various other factors. 
Treatments and products (including anti-aging creams) promising to reduce, remove, or prevent age-related wrinkles are big business in many industrialized countries. Despite great demand, most such products and treatments have not been proven to give lasting or major positive effects. Stretching the skin via a face lift will remove some wrinkles.
The wrinkles that occur in skin after prolonged exposure to water are sometimes referred to as prune fingers or water aging. This is a temporary skin condition where the skin on the palms of the hand or feet becomes wrinkly. It is caused when the keratin-laden epithelial skin is immersed in water. The skin expands and the resultant larger surface area forces it to wrinkle. Usually the tips of the fingers and toes are the first to wrinkle because of a thicker layer of keratin and an absence of hairs which secrete the protective oil called sebum. Wrinkled fingers often occur after taking a shower or bath and last up to fifteen minutes afterwards, until the water has evaporated or is absorbed into the body.
Prune fingers is named for the skins' resemblance to the wrinkled, rough surface of a prune.
Animals with wrinkles
Examples of wrinkles can be found in various animal species that grow loose, excess skin, particularly when they are young. Several breeds of dog, such as the Pug and the Shar Pei, have been bred to exaggerate this trait. In dogs bred for fighting, this is the result of selection for loose skin, which confers a protective advantage. Wrinkles are also associated with neoteny (cuteness), as they are a trait associated with juvenile animals.
Fabric wrinkles occur as a result of cloth being bunched or folded unevenly. Wrinkled clothing is often undesirable in situations such as job interviews, or formal social events. There are products such as irons and fabric sprays to remove wrinkles from cloth. Some more modern fabrics have been engineered to be wrinkle-free or wrinkle-resistant by incorporating water-resistant polymers.
- Grosz, David. Why Do Clothes Wrinkle? The U.S. Army faces its most pressing question, Slate.com, February 12 2007, retrieved February 12 2007.
- Anderson, Laurence. 2006. Looking Good, the Australian guide to skin care, cosmetic medicine and cosmetic surgery. AMPCo. Sydney. ISBN 0-85557-044-X.