Chafe is actually the breaking down of your most protective & developed top layer of skin (epidermis). This commonly occurs when your skin repetitively and continuously rubs against another item or object; this could your own skin rubbing together, tight and loose clothing rubbing against your skin, your skin interacting with a hard object such as a surfboard eg.bodyrash and shoes eg.blisters.
When the epidermis begins to be degraded, it is inflicted with micro-tears which accumulate and expand. As the epidermis continues to get damaged, it exposes undeveloped pink & red layers of skin tissues underneath. Our body attempts to repair itself by pumping blood to the damaged areas, this leads to swelling of the tissues and the formation of rashes... or chafing.