Normal wound healing takes about 3 weeks, but some wounds can take months or even years to heal. Local factors such as the condition of the wound, infection, trauma and edema affect healing as can systemic factors -- those that affect the whole body -- such as age, general health and nutritional status.
Contamination and Infection
Wound infection is one of the most common reasons for delayed wound healing. When a wound is contaminated or becomes infected, the immune system marshals energy to fight the bacteria, leaving little for healing. The bacteria produce toxins that also interfere with healing and cause cell death. Bite wounds are especially likely to be heavily contaminated.
Impaired Circulation and Oxygenation
Blood delivers oxygen and nutrients to the healing area and removes bacteria, toxins and debris. Conditions that reduce blood flow and oxygenation are common causes of poor wound healing. Advanced age, diabetes, peripheral vascular disease and high blood pressure can all affect circulation and interfere with healing. Anemia and chronic lung disease impair oxygenation, and obesity slows wound healing because fatty tissue has fewer blood vessels. Tobacco also impairs wound healing because it reduces circulation.
Condition of the Wound
The condition of the wound affects its ability to heal. Excessive pressure or repeated trauma to the wound delays healing. Dehydration causes the cells to dry up and crust over, whereas overhydration from exposure to urine or feces, for example, causes the skin to macerate -- become too moist and erode. Dead, or necrotic, tissue must be removed or the wound will not heal.
Drugs that inhibit the inflammatory response, such as corticosteroids, delay healing. Chemotherapy stops cells from proliferating, impairing wound healing. Radiation therapy depresses bone marrow function, increasing the risk of infection, and prolonged antibiotic therapy increases the risk for a secondary infection.
Elderly patients heal more slowly than children and healthy adults. Their skin is fragile and their risk of infection is higher because of a slower inflammatory response, diminished antibody production and slower endocrine system function. In addition, they are more likely to have chronic diseases such as diabetes and heart disease that impair circulation and oxygenation.
The body needs more protein and calories, zinc and vitamins A and C for wound healing, so a balanced diet is essential. Food plans should include at least two to three servings of protein, at least one serving of foods rich in vitamin A, such as green or orange fruits and vegetables and at least one serving of vitamin C-rich foods such as citrus fruits, strawberries, spinach, peppers, potatoes or tomatoes. Zinc, found in fortified cereals, red meat and seafood, may also be helpful for healing.