A poroma is a relatively rare benign adnexal neoplasm that originates from the intra-epidermal portion of the sweat gland duct (the acrosyringium). It is thought to arise from the eccrine sweat gland, but apocrine features may be seen. Eccrine poroma falls into the broader category of poroid neoplasms, or acrospiromas, which also includes the apocrine poroma, hidroacanthoma simplex, dermal duct tumor, and nodular, clear cell, and poroid hidradenomas.

Eccrine poromas occur only in the skin and most often present as a solitary, skin-colored or slightly erythematous, smooth or verrucous papule. They are less commonly pigmented or pedunculated. Poromas are usually less than 2 cm in diameter and are slow growing or fixed in size. Ulceration may occur, especially when over pressure points. Extremities, specifically palms and soles, are the most common sites, but they can occur anywhere; cases have been reported on the trunk, face, and neck. Rarely, patients may develop multiple poromas, or eccrine poromatosis. This condition is characterized by varying numbers of papules, more than 100 in some cases, that may be distributed widely or confined to the palms and soles.

Sweat gland tumors are thought to represent as little as 1% of primary cutaneous lesions, and poromas comprise only 10% of these. Poromas generally occur in adults over the age of 40, with no predilection for sex or ethnicity, and there is no apparent familial component. No definitive pathogenesis has been described, but cases have been reported as occurring in association with radiation exposure, trauma, pregnancy, hypohidrotic ectodermal dysplasia, and Bowen disease. They may also develop secondarily within a nevus sebaceus. Eccrine poromatosis has been reported in patients with lymphoproliferative disorders that have been treated with chemotherapy. Onset has varied from during the chemotherapy until years after.

Rarely, malignant eccrine poroma, or porocarcinoma, develops, either de novo or by transformation within a benign eccrine poroma. These lesions have metastatic potential.