Eczema and psoriasis, while often coupled together, have slight nuances that make them difficult to diagnose with a simple once-over (not to mention eczema and psoriasis can look totally different on different patients). So much so, that it usually takes a skin biopsy to figure it out: A doctor will remove a patch of infected skin to check out under a microscope; that way, they can measure the slight differences at the cellular level.
