Mouth irritants and irritating activities, such as smoking, often cause leukoplakia. Typically, cases of white patches in the mouth are harmless and symptoms resolve on their own. However, if the condition is leukoplakia, it can be associated with oral cancer. Chronic irritation seems to play a major role in most cases. Ongoing damage to oral tissues appears to cause them to enlarge, thicken, and often develop a substance called keratin. Keratin is a protein crucial to the health of the outer layer of the skin. Keratin provides the structure for skin cells and protects them from injury and stress. The protein is also key to wound healing. Small, white patches in the mouth are extremely common in response to minor injury and are typically not a sign of leukoplakia.