Quick Answer: Whites go grey from redeposited soil and detergent residue, not from staining. The three causes are overloaded machines, too much detergent, and washing whites with coloured items. Fix it by washing whites separately at 40 to 60C in a machine no more than three-quarters full, using the correct detergent dose, and skipping fabric softener entirely — softener coats fibres and holds greying agents in place.

The shirt is not stained. There is no mark you can point at. It is simply not white any more — it has drifted toward a flat, slightly dull grey that you only notice next to a new one.

So you wash it hotter, or add more detergent, or bleach it.

All three of those are, in most cases, actively making it worse — which is why the problem tends to accelerate once people start trying to fix it.

What is greying, technically?

It is soil that came off the fabric and then went back on.

Washing works by suspending soil in the water. Detergent lifts dirt off the fibres and holds it in suspension so it drains away. Greying happens when that suspension fails and the soil redeposits evenly across everything in the drum.

Even redeposit is why it reads as grey rather than as a stain. A distributed film of fine particles across a white surface lowers its reflectance uniformly. Your eye reads uniform reduced reflectance as grey, not as dirt.

The main causes of suspension failure are simple. Not enough water relative to fabric, not enough detergent to hold the soil, or too much detergent that does not rinse out and leaves a residue which itself attracts soil.

Hard water makes it substantially worse. Calcium and magnesium ions bind with detergent to form insoluble deposits that lodge in the fibres, dulling the fabric and reducing detergent effectiveness at the same time. In a hard water area this is often the dominant cause.

What are people doing wrong?

Five habits, and most of them are attempts to help.

Overloading the machine. The most common cause by a distance. Fabric needs water to move through it, and a packed drum means the soil has nowhere to go but back into the cloth. Three-quarters full is the working maximum — you should be able to fit a flat hand into the drum above the load.

Using too much detergent. Excess detergent does not rinse away fully. The residue stiffens the fabric, holds soil, and attracts more of it. Measure it rather than pouring, and reduce the dose if you have soft water.

Washing whites with light colours. Pale grey, cream and pastel garments release small amounts of dye every wash. It is not visible on them and it is cumulative on white. Whites need their own load, genuinely.

Using fabric softener. Softener works by depositing a thin cationic film on the fibres. That film is exactly what greying agents cling to, and it also reduces absorbency, so subsequent washes clean less well. Softener is the single worst product for whites.

Washing too cool. Body oils and sebum, which are the main soil on a shirt, do not emulsify well below about 40C. Cold-washing a white cotton shirt leaves oil in the fabric, and that oil then yellows and traps particles.

What actually restores and maintains white?

A short list, and the order matters.

Wash whites alone, at 40 to 60C, in a three-quarters-full drum. This alone resolves the majority of cases. Cotton shirting is designed for 60C and will not be damaged by it.

Use the correct detergent dose for your water hardness. If you do not know your hardness, your water supplier publishes it. Hard water needs more detergent or a water softener additive; soft water needs noticeably less than the pack states.

Add oxygen bleach, not chlorine bleach. Sodium percarbonate — the active in most oxygen bleach powders — brightens without weakening fibres. Chlorine bleach yellows cotton over time by reacting with residual detergent and with any protein soil, which is why bleached shirts often end up more yellow, not less.

Never use softener; use a white vinegar rinse instead if you want softness. Around 60ml in the rinse compartment removes detergent residue and mineral deposits, and the smell does not survive the cycle.

For a shirt already grey, strip it. Soak overnight in hot water with oxygen bleach and a small amount of washing soda, then wash normally. This works on redeposited soil and does nothing for dye transfer or chlorine yellowing, which is a useful diagnostic in itself — if the soak does not improve it, the cause was something else.

Myth vs Fact: Keeping Whites White

Myth: hotter is always better. Fact: 60C is the useful ceiling for cotton shirting. Above that you gain little and you set any protein soil — blood, sweat proteins, food — permanently into the fabric.

Myth: bleach is the answer for whites. Fact: chlorine bleach is a short-term brightener with a long-term yellowing cost on cotton, and it should not be used on any fabric with elastane or on wool at all. Oxygen bleach does the job without the trade-off.

Myth: line drying in sun damages white shirts. Fact: sunlight is a genuinely effective natural bleach on white cotton, and the UV exposure from occasional line drying does not meaningfully weaken it. Sun is the best free whitener there is — the caution applies to coloured fabrics, not to white.

Myth: the yellow under the arms is sweat. Fact: it is usually aluminium from antiperspirant reacting with sweat proteins and with the fabric. Ordinary washing does not touch it. Pre-treating with an acid — white vinegar or lemon juice — before washing does, and switching to an aluminium-free deodorant prevents it.

Myth: expensive shirts stay white longer. Fact: the fibre quality affects handle and durability far more than colour retention. A long-staple cotton shirt washed badly greys exactly as fast as a cheap one, which makes care the dominant variable at every price.

FAQ: White Shirt Questions, Answered

Can a grey shirt be brought back?

Usually, if the cause was redeposited soil. Soak overnight in hot water with oxygen bleach, then wash separately at 60C. Two rounds is not unreasonable. If there is no improvement after two, the cause is dye transfer or chlorine yellowing, and those are largely permanent.

How often should a white shirt actually be washed?

Every wear if it has been against skin all day. Body oil is the primary soil, and it oxidises and yellows if left in the fabric — a shirt hung up for a week between washes will develop yellowing that a washed one never does.

What about the collar and cuffs specifically?

Those are oil and friction points, so they need pre-treatment rather than a hotter wash. A little liquid detergent rubbed into the collar and left for ten minutes before the cycle handles most of it. Do this before the mark is visible, not after — visible collar grime is already partially set.

TL;DR:

• Greying is redeposited soil, not staining — caused by overloaded drums, wrong detergent dose, and washing whites with colours.
• Wash whites alone at 40 to 60C in a three-quarters-full machine. That fixes most of it.
• Skip fabric softener entirely and use oxygen bleach rather than chlorine, which yellows cotton over time.
• Underarm yellowing is antiperspirant aluminium, not sweat — pre-treat with an acid, and sunlight is the best free whitener available.

The pleasing thing here is that keeping whites white costs less effort than the strategies people use when they are losing the battle. No extra product, no hotter cycle, no bleach — just a separate load, a properly measured dose, and a drum with room in it. Get those three right and a good white shirt stays convincingly white for years.