Various types of bacteria, some that live normally and harmlessly on the skin, can become invasive and cause infection. Staphylococci ("staph") are frequent offenders; when they infect the scalp the result is often folliculitis (inflammation of hair follicles), with or without abscess formation. Skin is inflamed and painful around the infected follicles. Persistent folliculitis can lead to permanent hair loss. Treatment with antibiotics is usually necessary.
Viral scalp infection may be due to herpes simplex (the "cold sore" virus) or herpes zoster (the "shingles" virus). Symptoms may include folliculitis. Herpes zoster infection produces inflamed and extremely painful lesions on the skin-a classic symptom of shingles. Anti-viral medication may be prescribed after appropriate diagnosis