Stress

The skin's ability to heal, fight disease and close up wounds in compromised by tension, anger, depression, confusion and fatigue. People under stress are also more vulnerable to dermatologic conditions such as dermatitis.

Lack of Protein

Protein carries the building blocks for repairing the cells. If they leak out from an incision or a wound, they are lost, and unable to heal the skin.

Lack of Blood

Lack of blood to the area can cause skin to slow its ability to heal itself. Blood carries oxygen and nutrients to the cells, including skin cells, which help cells repair themselves. If the oxygen and nutrients are not there, then the cells are damaged and die.

Necrotic Tissue

Necrotic tissue is dead skin, and it is caused from disease or injury. If the necrotic cells aren't removed surgically or by debridement (cleaning of the area) then the new skin cells are unable to push their way to the surface and heal.

Disease

Diseases such as hemophilia, AIDS, or any disease that affects the clotting action of the blood, can damage the skin as well. The skin is unable to heal wounds because platelets are unable to clot the wound and stop the loss of proteins and blood which promote new skin cell growth.

Source:

Irish Health: Stress Stops Skin from Healing

Douglas Snider; Physical Therapist; Centre, Alabama