Cellulitis is a frequent medical skin infection caused by bacteria that can spread through the skin and connective tissues.The disease is an acute, painful and potentially severe infection of the skin and subcutaneous tissues.The borders of cellulitis are poorly demarcated.ErysipelasThis is essentially a superficial form of cellulitis that involves the upper subcutaneous tissues and dermis.This makes it very difficult to differentiate cellulitis from erysipelas medically.In erysipelas, borders of infection are clearly demarcated.The appearance is that of a fiery red rash that can be painful.Erysipelas is also called St Anthonys fire.This name is from the Egyptian healer of the middle Ages who had been able to cure it.What are the causes of Cellulitis?Risk factors for infectionThey are more frequent and more severe in patients with underlying diseases such as:1. Diabetes,2. Cancer3. ImmunodeficiencyOther risk factors for cellulitis are:1. Cracks or peeling skin between the toes2. Venous insufficiency or history of peripheral vascular disease3. Injury or trauma with a break in the skin or skin wounds or abrasions4. Insect bites and stings, animal bites, or human bites5. Ulcers from certain diseases including diabetes and vascular disease6. Use of corticosteroid medications or medications that suppress the immune system7. Wound from a recent surgery8. Previous erysipelas or cellulitis.9. Elderly age.10. Alcoholism11. Intravenous drug use.12. Lymph edema.13. Obesity.14. Inflammatory dermatoses.15. Pregnancy.Causative organismsCellulitisMajority of infections that involve intact skin are believed to caused by streptococci, although many other micro-organisms may be responsible if the skin integrity is compromisedInfrequently, Gram-negative bacteria, anaerobes or fungi may produce cellulitis.These organisms are more frequent causes in children, people with immuno-compromised patients and in diabetes.Cellulitis happening around surgical wounds less than 24 hours post-operatively may result from group A beta-hemolytic streptococci or Clostridium perfringens.The latter produces gas gangrene, resulting in crepitus on examination.ErysipelasMajority of infections are with group A streptococci but Streptococcus pneumoniae, Klebsiella pneumoniae, Yersinia enterocolitica, Hemophilus influenzae type b, and Moraxella spp. have been found.Rarer causative organismsInfrequently, cellulitis or erysipelas may be produced by other organisms:1. H. influenzae type b - in children less than 6 years of age.2. Pasteurella multocida, Streptococcus anginosus (formerly known as Streptococcus milleri), and3. Capnocytophaga canimorsus - following cat or dog bites.4. Vibrio vulnificus, Aeromonas hydrophila - following sea or fresh-water exposure.5. Erysipelothrix rhusiopathiae - in butchers, vets or fish handlers.6. Mycobacterium marinum - in aquarium keepers.It is therefore important to find out the patients occupations in poorly healing infections.The most frequent causative organisms are Streptococcus or Staphylococcus species but they can be due to a wide range of both aerobic and anaerobic bacteriaNormal skin has many forms of bacteria living on it.When there is a break in the skin, these bacteria can produce a skin infection.The most frequent locations of cellulitis were the legs and toes, followed by the feet, hands, face, torso, neck, and buttocks.Skin in the infected area will become red, hot, irritated, and painful.Cellulitis is more frequently observed in the lower limbs and normally involves one limb.In many patients, there is an obvious precipitating skin lesion, such as a traumatic wound or ulcer, or other area of damaged skin - e.g., athletes foot.There is erythema, pain, swelling and warmth of affected skin.