common, 1-3% population
Malassezia ovale
red lesions with distinct margin and greasy scales, face, chest, flexures, scalp (maybe dandruff) (not hair loss), NOT usually itchy
risk factors - immuno-deficient, neuro or cardiac disease, alcoholic pancreatitis

Mx - antifungal creams / shampoos (ketoconazole 2% x2/wk for 2-4/52) or tar shampoo - both occasionally cause itch, burning, tightness, erythema
steroids (topical - can come in lotion / mousse)

DD
Psoriasis
Eczema
Tinea - alopecia with scales - may have LN
Head lice
Allergic contact dermatitis - often on hands (thick, red, cracked) and related to occupation
Guttate psoriasis - children / adolescents - red tear drops on trunk and limbs - 2-4 weeks post strep throat
Flexural psoriasis - esp HIV and alcoholics - red patch - hard to treat - beware prolonged steroids in flexure

Kerion
severe pustular eruption with alopecia 
from advanced fungal disease and exaggerated host response
large, painful, inflammatory, boggy, purulent plaques (pus comes on squeezing from multiple sites) with local LN