Both cellulitis and erysipelas start and spread quickly, and cause redness, swelling, pain, and warmth. People who have one of these infections may feel worn out and sick, and have a fever. In severe cases of cellulitis, widespread symptoms of infection may appear, including fever, chills, low blood pressure, rapid breathing, and rapid heartbeat.
The common form of impetigo begins with a small (2-4 mm/.04-.16 in) reddened, flat area of skin (macule) that rapidly forms either a clear or pus-filled blister (vesicle or pustule). These blisters are fragile and rupture easily, releasing a fluid that dries into a golden crust. The sores itch, and scratching them causes the infection to spread to other areas. The wounds take a while to heal, but do not leave permanent scars. In the bullous form of the disease, which is less common, the blisters are larger, tense, and filled with a clear fluid. People with this form of impetigo may also have a fever, diarrhea, and general weakness—symptoms not found in common impetigo.
Skin infections accompanied by cell death (necrotizing infections) often cause pain, fever, malaise, and a dark swelling of the affected area. As the infection progresses, the skin will become darker, moving from deep red to blue or black—a signal that it has become gangrenous. Bullae, or large blisters filled with dark fluid, may appear. The infection spreads rapidly in underlying tissues, which is not apparent from the appearance of the overlying skin.
Certain conditions that impair circulation or immunity predispose people to skin infections such as cellulitis. These conditions include:
- Disease of the blood vessels in the arms or legs (arteries or veins) or conditions that worsen the circulation, such as heart failure
- Age (the very young and the elderly are at greater risk)
- Recent surgery or childbirth
- Chronic skin conditions that cause breaks in the skin (i.e., eczema)
- Intravenous (IV) drug abuse
- Cirrhosis (advanced liver disease)
- Systemic cancers, especially if treated with chemotherapy or radiation
- Athlete's foot
Skin and soft-tissue infections such as cellulitis are more common among people whose immune systems are not working properly, such as those with cancer. An impaired immune system makes a person less able to fend off disease, and when infected, less capable of controlling an infection. For cellulitis, some of these immunosuppressed states might include diseases such as cancer, but also therapy for cancer or immunosuppression for transplant surgery.
In addition, some diseases make the skin and underlying tissues more vulnerable to bacteria by slowing blood flow. Diabetes is in this category. Removal of the saphenous vein in the leg for bypass surgery also can cause swelling (edema) and poor blood flow. As a result, the skin may break open. Those who have had recent surgery or other trauma to tissues (such as childbirth or an accident) may expose normally sterile tissues to bacteria, making cellulitis more likely.
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