Sweating is a fact of life. Everyone sweats, whether due to hot weather, strenuous exercise, anxiety or fever. But what does it mean when your sweat appears to take on a yellow hue?
Read more: 6 Things Your Sweat Can Tell You About Your Health
Sweating is how your body self-regulates its temperature and cools itself down, notes the U.S. National Library of Medicine (NLM). "The purpose of sweat is to maintain a relatively stable internal body temperature when we are in a hot environment and/or performing exercise," explains S. Tony Wolf, a research fellow at the Center for Healthy Aging at Penn State University in University Park, Pennsylvania.
"Sweat is excreted from sweat glands in our skin, and that sweat is evaporated by the air around us," Wolf says. "And when that evaporation occurs, it causes heat to be dissipated from our skin and the skin to be cooled. At the same time, blood flow is increased in the small blood vessels in the skin."
"Because the skin is being cooled through evaporation, skin temperature is lower than internal body temperature," he adds. "Therefore, as blood passes through those skin blood vessels, it is cooled before being circulated back to the body's core, in turn acting to reduce core temperature."
Sweat is naturally clear, notes the NLM, and Wolf says that's "because sweat is primarily water."
"It contains some electrolytes like sodium and potassium, as well as small amounts of other metabolites," he says, adding that it's derived from blood plasma, which constitutes more than half of all the blood in your body.
When Sweat Turns Yellow
But when your sweat takes on a yellowish color, is it cause for concern? That depends, "When referring to 'yellow sweat,' there is a distinction that must be made," Wolf says.
"Some may notice that sweat sometimes appears yellow on their clothes. In most cases, this is explained simply by the fact that sweat mixes with various bacteria in the skin, as well as other compounds found in deodorant and even in clothing, causing the sweat to take on a yellowish tint. The sweat itself, however, is colorless. For most people who notice yellow sweat stains on their clothes, this is the likely explanation."
But if your actual sweat has taken on a color of its own, a few rare conditions could be to blame. These include:
Apocrine chromhidrosis. According to a research published in the Dermatology Online Journal in March 2012, this rare but chronic disease has no clear cause, typically strikes during puberty and usually affects only the face and armpits. Its defining feature, the study says, is colored sweat — driven by the secretion of yellow-brown pigment granules called lipofuscin.
"The sweat is commonly yellow," Wolf says, "but it can also take on other colors. Treatment, the study notes, may include administration of a 20 percent aluminum chloride hexahydrate solution, followed by capsaicin cream, but relapses are not uncommon once treatment subsides.
Eccrine chromhidrosis. According to a case study published in Annals of Dermatology in August 2015, this very rare and difficult-to-diagnose condition stems from water-soluble pigments from drugs or dyes that are expelled via your eccrine sweat glands, causing yellow-, brown- or even green-tinted sweat. (Eccrine sweat glands are those that open directly onto your skin's surface, over most of your body, explains the Mayo Clinic.)
According to the case study, the color change could be the result of foreign chemicals on the skin's surface or contamination by bacteria or fungi reacting with sweat gland secretions.
Pseudochromhidrosis. This disorder creates sweat that's red or black in color, according to a case study published in the July/August 2016 issue of the Indian Journal of Dermatology. When this condition develops, the study explains, initially colorless sweat ends up becoming pigmented after making contact with bacteria, paints, dyes, fungi or food particles on the skin's surface.
The good news? The study stresses that this issue is likely brought on entirely by external factors rather than any dysfunction going on inside the body's sweat production process — and it's easily treatable, simply by identifying and removing the trouble-making bacteria, fungi or chemical.
Is This an Emergency?
- S. Tony Wolf, PhD candidate and research fellow, Center for Healthy Aging, Penn State University, University Park, Pennsylvania
- U.S. National Library of Medicine: “Sweat”
- Dermatology Online Journal: “Facial and Axillary Apocrine Chromhidrosis”
- Annals of Dermatology: “Eccrine Chromhidrosis Resembling Clinical Features of Pompholyx With Bile-Like Greenish Pigmentation on the Right Palm and Soles”
- Indian Journal of Dermatology: “Red and Black Pseudochromhidrosis”
- Mayo Clinic: "Sweat Glands"