Fungal infection on thumbs and index finger?

Examine on video, or: Examine in-person. A scaly sore with rounded edges can be ringworm, which is caused by a fungus, and the rash is called tinea corporis. Eczema rashes and psoriasis rashes can also cause a round scaly sore and look like ringworm. A primary care doctor or dermatologist can evaluate to make a diagnosis (as the disorders can look very similar) and discuss the treatment of one's particular diagnosis.