There are two main types of sweat glands: apocrine and eccrine.
Apocrine sweat glands continuously secrete a fatty sweat into the gland tubule of the hair follicle. Emotional stress causes the excretion of the fatty acids to the skin, where local bacteria break it down into odorous fatty acids. This is where a lot of your body odor comes from. Apocrine glands in the breast secrete fat droplets into breast milk and those in the ear help form earwax.
In human beings, apocrine glands are concentrated in the underarm and in genital regions; the glands are inactive until they are stimulated by hormonal changes in puberty. Apocrine glands are found at our armpits, nipples, ear canals, eyelids, and wings of the nostril. Modified apocrine glands include the ciliary glands in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce milk.
Eccrine glands are the major sweat glands of the human body, found in virtually all skin. They are very concentrated in palms and soles, and then on the head. In lower mammals, they aren’t very common, being found mainly on hairless areas such as pads of the feet.
Eccrine glands produce a clear, odorless liquid, consisting mostly of water and NaCl. NaCl is reabsorbed in the duct to reduce salt loss of the body. They are active in thermoregulation by helping to cool the body through water evaporation of sweat secreted by the glands on the body surface.