There are many causes for wrinkles; many are based on biological factors or environmental factors. As humans age, skin loses its elastic quality because skin cells of the dermis multiply more slowly, fat cells under the dermis degenerate, and the layers of elastin and collagen loosens. Skin becomes dry because of the break down of sweat-and oil-secreting glands.

Stimuli, such as the sun's rays, cause frowning and therefore form lines. Habitual facial expressions are also responsible for wrinkles. These facial expressions are a result of muscle contraction, which is caused by electrical impulses sent from the brain to the muscles. This electrical impulse is sent to the muscle via the neurotransmitter, acetylcholine.