White T-shirts and how they stay white

Short answer: White turns grey from colour transferred by other laundry and yellow from sweat and deodorant, and these two problems occur completely independently of each other. Each has its own fix, and heat makes both worse if you are not careful.

Wash white on its own

Even a single light grey or pale blue item releases enough dye over time to grey a whole load, even at low temperature. Keep white laundry completely separate every single time, no matter how little of it there is. See washing and care.

Yellow stains in the armpit

They occur when sweat and aluminium salts from deodorant react chemically with each other in the fabric over time. Treat the stains before washing with a stain remover, because dryer heat sets them permanently if you skip that step. See bamboo T-shirts for men.

Oxygen-based rather than chlorine

Chlorine bleach makes viscose fibres brittle over time and can actually turn the fabric yellow instead of whiter. Use an oxygen-based bleach instead, which is far gentler on the fibres while still removing most stains effectively.

An undershirt prevents it

A layer under the T-shirt catches sweat before it ever reaches the T-shirt and the armpits at all. It is the simplest prevention against yellow stains and requires no extra effort in the wash afterward. See bamboo undershirt for men.

Not in the dryer with stains

Dryer heat sets discolouration permanently, so it can never be washed out again afterward no matter what you try. Always check clothes for stains before they go in the dryer, and wash again if you are unsure. See bamboo T-shirt for women.

The sun bleaches naturally

Hanging white laundry to dry in direct sunlight actually helps lighten the fabric slightly over time. It is a free and gentle method, but it works slowly and needs several sessions in the sun for a visible effect.

A full machine gives a worse result

An overloaded machine cannot rinse soap and dirt properly out of the laundry, and white clothes show that more clearly than most other colours. Wash white in smaller loads than usual, and the result becomes noticeably better.

Baking soda as extra help

A couple of tablespoons of baking soda in the wash can help neutralise odour and loosen light discolouration without straining the fibres unnecessarily. It is a cheap supplement, not a replacement for a proper stain remover on tough stains.

Check the water temperature regularly

Most washing machines allow up to 60 degrees for white cotton, but bamboo viscose tolerates less heat than that. Stick to 30 to 40 degrees, even for white, to protect the fibres over the long term.