Apocrine carcinomas occur anywhere apocrine sweat glands are found, so it's easy to see what parts of the body are at risk -- just look for the hair follicles. The scalp is a particularly common site of the cancer, which originates from the apocrine sweat glands. However, the cancer can crop up on the genitals, arms or any other place hair follicles grow from the skin [source: Chintamani]. Although less commonly, the term apocrine carcinoma is also used to refer to a rare form of breast cancer that forms in the ducts and makes its presence known with apocrine secretions [source: Japaze].
Apocrine carcinomas first appear as firm cysts right under the skin, which has usually turned red or purple in that distinct spot. There may be one cyst or many. The problem, especially when it comes to treatment, is that it's easily spread from this localized area to the lymph system, and then throughout the body. So, not only does the cancer eat away the tissue near the apocrine glands where it first appeared, but it can do some serious damage in other regions of the body as well. For example, even if an apocrine carcinoma develops in the armpit, it can send cancerous cells to the brain [source: Chintamani].
This isn't usually a young person's disease. In most cases, apocrine carcinoma is diagnosed in older adults. Fortunately, however, it is exceedingly rare. Fewer than 40 cases have been reported worldwide [source: Chintamani]. However, recent research suggests this type of cancer is on the rise in the U.S. An aging population with a lifetime of ultraviolet sun exposure may be to blame [source: Donaldson-Evans].
In the end, apocrine sweat glands offer more to consider than a few basic hygiene rules. Although not visible to the naked eye, these tiny glands can cause big problems if something goes awry.