Sweat marks under the arms and what reduces them
Short answer: Sweat marks appear when moisture reaches the outer layer. A thin base layer that catches the sweat keeps the shirt dry, and it is the only method that works consistently, however much you sweat.
Why the marks appear
Sweat under the arms has a short way to the fabric, because the armpit is warm and closed when your arms hang down. If the shirt touches the skin directly, it absorbs the sweat and the mark spreads outwards. The denser and smoother the fabric, the sharper the edge of the mark.
A layer under the shirt
An undershirt with short sleeves covers the armpit and catches sweat before it reaches the shirt. A tank top does not do the same, because it does not cover that area. Choose a thin style that lies smooth under the shirt without creasing. See bamboo undershirts for men.
Sleeve length matters
The sleeve should reach well below the armpit, or sweat runs past the edge and into the shirt. An undershirt that fits close to the body keeps the fabric in place best when you lift your arms. Check in the mirror that the sleeve does not show under a short sleeved shirt.
The outer layer fabric
Dense synthetic fabrics show marks most clearly, because moisture gathers in one spot. Bamboo viscose spreads moisture over a larger area and dries faster, so the mark is less visible and fades sooner. That also applies when the T-shirt is your outer layer. See bamboo T-shirts for men.
Colour matters a lot
Navy and black hide marks best. Light grey shows them most clearly of all colours, more than white, because the damp patch turns much darker than the rest of the fabric. Mid tones with a pattern or texture also hide more than plain, smooth single colours.
Fit around the armpit
A shirt or T-shirt that is tight at the armpit presses fabric against the skin and absorbs more sweat. A little room in the armhole gives air and reduces contact. At the same time there should not be so much fabric that it folds, because folds hold on to moisture.
Washing does not remove build up
Yellow build up in the armpit comes from sweat and deodorant together. It must be treated before washing, not after, because the heat of the machine sets it in the fabric. Wash shirts and T-shirts inside out so the armpit gets the most water. More tips under washing and care.
Deodorant and timing
Let deodorant dry completely before you get dressed. Wet deodorant goes straight into the fabric and adds to the build up. Some people apply it in the evening so it has time to work. What suits you depends on the product, so read the instructions on the packaging.
When it is more than heat
If you sweat heavily under the arms without a warm reason, or it affects your daily life, talk to a doctor. Treatments exist, and clothing can only make it easier to live with. An undershirt and the right colours help, but they do not remove the cause.
Frequently asked questions
Which colour hides sweat marks best?
Navy and black. Light grey shows them most clearly of all colours, more than white, because the damp patch looks much darker than the rest of the fabric.
Does an undershirt help against sweat marks?
Yes, if it has sleeves that cover the armpit and reach a little way down. A tank top does not cover that area, so it does not help with the marks.
Can yellow stains in the armpit be removed?
Only if they are treated before washing. The heat of the machine sets them in the fabric, so they cannot be washed out afterwards, however many times you try.
You can find the full range at Bamboo-Clothing.com.
