Clobetasol should not be used to treat toenail fungus, but it may be used to treat toenail psoriasis, which in some cases may resemble toenail fungus. Around 30% of people with nail psoriasis may also have a fungal infection. Using clobetasol alone to treat toenail fungus may cause the toenail fungus to worsen and spread to other nails.

The symptoms of nail fungus and nail psoriasis can look quite similar. In both, the nails look pitted, thickened, or deformed. People with nail psoriasis are likely to have psoriasis on other parts of their body and their nails may detach from the nail bed creating a gap that can be infected by bacteria. They often have a chalky build-up under their nail that causes the nail to lift. Fungal nails are common and usually start white or yellow spot under the edge of a fingernail or toenail. Often people also have athlete’s foot (tinea pedis).

Nail psoriasis affects up to 90% of people with psoriasis at some point in their lives. Research has shown that 8% clobetasol nail lacquer applied twice a week to psoriatic nails effectively penetrates the nail and reduces both nail bed and nail matrix abnormalities, with fewer side effects than clobetasol cream (which can be systemically absorbed).