Yellow marks under the arms

Short answer: Yellow marks under the arms come from sweat mixed with aluminium from deodorant. It is not ordinary dirt, which is why more detergent does not help. There is a lot you can do to prevent them, though, so your top keeps its colour longer.

Deodorant is the source

Aluminium in deodorant binds to the fibres and turns yellow over time. It happens gradually, so you only notice once the stain is already clear. Try a version without aluminium, and wear a thin layer between your skin and the top, for example a bamboo tank top for men. Then the deodorant does not reach the top directly.

It is not dirt

Many people try to wash the stain out with more detergent or a stronger programme. That does not work, because the discolouration is not loose dirt. It is a reaction that has set in the fibres themselves. So it is about prevention, not about scrubbing harder once the stain is there.

Let the deodorant dry

If you put your top on right after applying deodorant, much of it transfers straight to the fabric. Wait a few minutes until it is completely dry. Apply it in the evening or right after a shower, so some time passes before you get dressed. That reduces the amount that ends up in the fabric.

A layer in between helps

An undershirt between your skin and the top catches most of it. The innermost layer takes the sweat and deodorant and can be washed often without it mattering. The top stays good looking much longer. Look at bamboo undershirts for men, which are made to sit close under a shirt or jumper.

Wash before the stain sets

Wash the top after every wear in warm periods. The longer sweat and deodorant stay in the fabric, the more they bind. A top left hanging with sweat in it for two days is far harder to keep white than one that goes in the wash the same evening. This matters most for light bamboo t-shirts for men.

Washing hotter is not the answer

It seems logical to wash hotter to get the stain out, but heat can actually fix the discolouration. Wash promptly after wearing at forty degrees instead. That temperature removes sweat without making the stain worse. Always follow the care label on the garment.

Summer is the worst

In summer most people sweat more, and clothes are worn for many hours in the heat. That is why yellow stains often appear over the course of a summer. Change tops more often in the warm months and wash them straight away. Then the sweat has no time to set.

Dark colours hide it

Yellow marks show most clearly on white and light clothes. On dark colours the same reaction can leave pale or stiff patches instead. If it keeps happening, it can make sense to wear darker tops on the hottest days and save the white ones for cooler weather.

Frequently asked questions

Why does white clothing turn yellow under the arms

Because sweat reacts with aluminium from deodorant, and the reaction sets permanently in the fibres, so an ordinary wash cannot remove the stain.

Does washing hotter help

No. Heat can actually fix the discolouration. Wash promptly after wearing at forty degrees instead, and always follow the care label.

How do you prevent it

Wear a thin layer under the top, let the deodorant dry fully before you dress, and wash more often in summer when you sweat the most. Those three things together solve most of the problem.