What causes small cracks to form on a recently painted wall?

This problem is commonly called “alligatoring.” The most common cause of alligatoring is the application of too thick of a paint film. The surface of the film dries first, with the rest of the film taking longer to dry than normal. When the underside of the paint finally does dry, it shrinks, causing the top of the film to pull apart and leaving unsightly cracks. You can prevent this by applying the paint at the manufacturer’s recommended thickness and spreading rate. A less frequent cause of alligatoring results from painting over a contaminant on the surface such as oil, silicone, body oils, hair spray, etc. You can prevent this by thoroughly cleaning the surface before painting.