Most of the sweat glands of the body belong to the eccrine (merocrine) variety. These sweat glands begin to develop at about 20 weeks as solid cylindrical epidermal downgrowths that are more compact than those of hair primordia and do not develop mesen-chymal papillae at their bases. As the bud elongates, its end becomes coiled on itself to form the primordium of the secretory part of the gland. The uncoiled, proximal part of the bud forms primordium of the gland duct. The central cells of the epithelial bud degenerate during the 7th month to form a lumen. In the secretory portion, the peripheral cells become differentiated into two layers: an inner layer of secretory cells and an outer layer of myoepithe-lial cells. The eccrine sweat glands begin to function soon after birth.
The apocrine sweat glands are large, specialized sweat glands which develop in certain region of body, e.g. axilla, areolae of the nipples, pubic and perianal region. Primordia of these glands appear as buds which originate from the sides of the hair follicles. Consequently, the ducts of apocrine sweat glands do not open directly onto the skin surface but into the upper part of the hair follicles just above the openings of the sebaceous glands. These glands do not produce secretion during childhood and become functional at the time of puberty