Cellulitis is a deep bacterial infection of the skin and infection usually on the face, or the arms and legs. It may happen in persons with normal skin, but it usually occurs after some type of trauma cause of skin opening and infection.

Causes: 

• Bacterial infection of a wound or area of skin that is no longer intact. 
• Most common bacterial causes of cellulitis include the following: Group A - haemolytic streptococcus, Streptococcus pneumonia and Staphylococcus aureus
• Other causes may include human or animal bites, or injuries that occur in water.

Symptoms:

• The following are the most common symptoms of cellulitis. It may vary person to person and common symptoms are:
• Swelling of the skin
• Tenderness
• Warm skin
• Pain
• Bruising
• Blisters
• Fever
• Headache
• Chills
• Feeling weak
• Red streaks from the original site of the cellulitis

Some cases of cellulitis are considered an emergency. Always consult your physician immediately if you notice any of the following symptoms:

• Inflamed skin and red rash
• Fever
• Numbness, tingling, or other changes in a hand, arm, leg, or foot of affected area
• Skin turns black
• Red and swollen  around your eye(s) or behind the ear(s)
• Diabetic or have a weakened immune system 
• The symptoms of cellulitis may resemble other skin conditions. Always consult your physician for a diagnosis

Diagnosis:
Diagnosis is usually carried out after study of medical history and physical examination. Blood and skin samples may be taken to confirm the diagnosis and the type of bacteria that is present.