Non-healing or slow healing wounds are usually infected or contain foreign material such as wood or dirt, dead or sick tissue, or dead bone (sequestrum).

Proud flesh (excessive granulation tissue) is both a sign and a cause of poor healing. It is the body's attempt at "plugging the hole". When above the level of the skin, it can stop the progress of further healing by blocking the passage of skin cells migrating in from the sides of a wound (the process called epithelialization).

Wounds may actually seem to enlarge for the first week or so after they occur. This is normal during this early stage of wound healing, especially in situations in which there has been excessive tissue damage to the wound edges. The body liquifies the damaged tissue to allow healthy tissue to bridge the defect. Slow or non-healing wounds are most commonly found on the lower limb, particularly in high motion areas such as the fetlock and hock, and overlying the flexor tendons.