The most common skin infections are caused by Staphylococcus aureus, group A streptococci (Streptococcus pyogenes), or the normal skin flora. An antistaphylococcal oral antibiotic is the preferred treatment for nonbullous and bullous impetigo, and a therapeutic agent that is effective against both S aureus and streptococci is appropriate for most cases of cellulitis. For furuncles, carbuncles, cutaneous abscesses, and inflamed epidermal cysts, the most important therapy is incision and drainage, and in most cases there is no need for antimicrobial therapy. Patients with venous ulcers and atopic eczema do not benefit from systemic antimicrobial therapy unless obvious infection is present, as indicated by clinical features such as fever, cellulitis, and lymphangitis.