How can you distinguish between nodular melanoma and a pimple?

Different: A pimple is a small skin nodule usually secondary to inflammation , possibly associated with pus and usually small in size with possible erythema. A nodular melanoma is a progression in development of the classic skin melanoma, mostly pigmented and firm with the irregularity in the underlying tumor pigmentation. Rarely it is associated with amelanotic melanoma.

Time or biopsy: A pimple should come to a head and gradually heal within 7-10 days. Nodular melanoma will not go away in this time period. If there is still a concern, a biopsy will give a definitive answer by its appearance under the microscope.