We have all experienced the dread of getting sweat stains on our clothing at some point in our lives, especially during the summer, and seemingly right before important events and presentations. Beyond ruining your day, sweat stains can even ruin your clothing. White-colored clothing is especially prone to discoloration in the underarm and collar region, where we often sweat from the most. Sometimes all it takes is a couple of wears, and suddenly our white shirts have yellow stains.
It is important to understand that there are two types of sweat glands on the human body: the eccrine and apocrine glands. The eccrine glands are all over the body and secrete a colorless and odorless sweat, that is essentially salt water. The eccrine glands are present in high numbers on the palms, soles, and head, which explains why hyperhidrosis sufferers often sweat excessively from these zones. The apocrine glands, on the other hand, develop in relation to hair follicles meaning they are present in areas with the most body hair, such as the underarms. They secrete a thicker sweat that contains fats and proteins that is responsible for body odor (bromhidrosis) when it encounters bacteria on the skin, which breaks it down and releases a foul-smelling odor. While different in composition than eccrine sweat, apocrine sweat is also colorless.
Besides leaving salt marks on clothing, sweat itself cannot stain or discolor clothing as it is colorless. The culprit behind those yellow stains on your white shirts is your antiperspirant, not yellow perspiration. What gives sweat that yellow tinge is when the minerals in your sweat (mostly salt) come into contact with your aluminum-containing antiperspirant. This creates a chemical reaction, which reacts with the fiber in your clothing and can result in yellow stains on clothing. So, your antiperspirant is to blame, not your sweat!
We have established that sweat is generally colorless, however, some people do sweat colors. This is an extremely rare condition called chromhidrosis (chrome = color, hidrosis = sweating). There are two types of chromhidrosis: apocrine and eccrine chromhidrosis, which are differentiated based on which sweat glands are affected.
Apocrine chromhidrosis is caused by the presence of lipofuscin (a yellowish-brown pigment) that is not meant to be found in the sweat glands. The cause of this is still unknown to scientists, but essentially this pigment makes its way into the apocrine glands where it oxidizes (which can give it a different color) and is then excreted out with the sweat. Depending on the level of oxidization, it can cause black, blue, green, brown, red, and yellow sweat. Research on the topic is quite limited, and no cure or effective treatment for the condition exists.
Eccrine chromhidrosis is caused by the ingestion of certain dyes, chemicals, or drugs, which then find their way into the eccrine glands and where they are excreted with the sweat. Cases of red, yellow, and blue excretions have been documented. This type is treatable by identifying the color-causing agent and removing exposure to it.
Another more common type of the condition is called pseudochromhidrosis (pseudo = not genuine), which is when sweat becomes colored when it comes into contact with something on the surface of the skin. Therefore, in this case, the sweat was not colored when leaving the body but has been given its color by encountering something on the skin (dyes, chemicals, etc.). This is the more common type of the condition, and this one can easily be treated by identifying what is causing the sweat to become colored on the skin and removing exposure it.
So, unless you are one of the very few people who suffer from true chromhidrosis, your sweat is colorless but can react with certain dyes and chemicals and appear to be colored. What we can take from this is that no one sweats the same: some sweat excessively (hyperhidrosis), and some sweat in different colors (chromhidrosis).