Folliculitis is an inflammation of the hair follicle. This presents with small red bumps overlying the opening of the hair follicle. Folliculitis can be caused by both bacterial or fungal infection. They can look quite similar in appearance.
Psoriasis is a chronic skin disease which presents with thick scaly pink or red plaques on the body. It can often present with scaling of the scalp too which looks like dandruff. The commonest form of psoriasis is psoriasis vulgaris. In psoriasis vulgaris, the plaques are large and raised with thick overlying scales. Common sites of involvement are the elbows, knees, umbilical area and scalp but just about any part of the body can be affected. This is very different in appearance from folliculitis which presents as tiny red bumps.
There is a variant of psoriasis called guttate psoriasis. This presents with small scaly spots often on the trunk and limbs. Though smaller, they are still larger and scalier than the bumps seen in folliculitis.
If you have any doubt about your rashes, do see your doctor or dermatologist for a proper assessment and diagnosis.