Scalp Rashes That Aren't Psoriasis
Scaly red rashes on the scalp can be caused by seborrheic dermatitis, also known as dandruff. The difference is that psoriasis of the scalp often has significant thickening of the skin and thick adherent scales. Seborrheic dermatitis usually just has some pinkness of the skin of the scalp with much finer scales. Seborrheic dermatitis often involves the eyebrows and the sides of the nostrils as well, so sometimes involvement of these areas will help to separate this disease from psoriasis.
Fungal infections of the scalp are not so rare in children and so a child with a scaly scalp may have fungus, psoriasis or seborrheic dermatitis. Hairs can be plucked and examined under a microscope to help confirm a diagnosis of fungus.
Flexural Area Rashes that Aren't Psoriasis
In the creases of the armpits and groin area, as well as under breasts, the increased moisture present tends to macerate scales creating a pasty white substance. Redness and maceration can be seen with both psoriasis or candidiasis (common yeast infection). A dryer red rash with scales around the edges is typical of tinea cruris or "Jock Itch". A darker discolored patch in this area without scaliness may be erythrasma, a minor bacterial infection. Your dermatologist can examine skin scales or debris under a microscope or use an ultraviolet light called a Wood's Light to help differentiate these rashes from psoriasis.
Hand and Foot Rashes that Aren't Psoriasis
Hand and foot rashes may be the most difficult to differentiate from true psoriasis. Eczema, fungal infections, allergic reactions and irritation from chemicals can all cause changes which may be confused with psoriasis. Most of these rashes cause thickening, redness and scales on the backs of the hands or feet but may cause a blistering rash on the palms and soles. Nail changes can occur in fungus or severe eczema involving the cuticle areas. Skin biopsies from hand and foot rashes can be confusing and often show mixed features in the same specimen. Differentiating hand and foot rashes from psoriasis requires significant skill and usually necessitates examination of other body parts, ie: scalp, elbows, knees, to look for clues.