Picks
Almost nobody's white shirts are killed by wear. They are killed at the collar and the underarms, by a chemical reaction most people are actively making worse, and then finished off in the wash.
Worth understanding, because two of the three things that ruin a white shirt are entirely avoidable and the third is mostly a question of what the cloth was made of in the first place.
The yellow is not sweat
Start here, because it changes everything that follows. Sweat is essentially colourless. It is water, salt, urea, amino acids and, from the apocrine glands under your arms, a quantity of protein and fat.
What turns yellow is the reaction between those proteins and the aluminium compounds in antiperspirant. Nearly every antiperspirant on the market works by dissolving aluminium salts in your own sweat to form a gel that plugs the sweat ducts. That gel does not stay put. It transfers to the cloth, dries, hydrolyses into aluminium hydroxide, and over repeated wear-and-wash cycles complexes with the amino acids and lipids in sweat to form compounds that are progressively yellower and progressively less soluble.
Body heat drives it. The underarm sits at 35 to 37°C all day, which is close to ideal conditions for the cross-linking that binds the whole mess to cotton cellulose.
The practical test is simple. Aluminium-free deodorants do not produce this. If your shirts yellow under the arms, that is your antiperspirant plus your own proteins, not poor hygiene and not cheap fabric.
The ring around the inside of the collar is a different animal. That is sebum, the oil your skin produces, plus dead skin and whatever is in the air. It oxidises slowly and goes tea-coloured, and unlike the underarm stain it is a straightforward greasy soil that responds to ordinary degreasing.
Bleach makes it worse, reliably
This is the part that catches almost everyone, because chlorine bleach is the instinctive response to a yellow mark on something white.
When hypochlorite meets protein that is already bonded to aluminium, it does not lift the stain. It sets it. The reaction produces a cross-linked compound bound tightly to the cotton, and a mild yellow becomes a dark permanent one. Textile extension services and long-serving dry cleaners have been saying this for decades, and the American Cleaning Institute advises against chlorine bleach on antiperspirant-stained garments.
Chlorine bleach also attacks cellulose directly. Every cycle with it shortens the fibre, weakens the cloth, and leaves the shirt more prone to yellowing on the next round. It is a genuinely destructive habit dressed up as maintenance.
Heat does the same job by a different route. A hot dryer or a hot iron drives residue deeper into the fibre and accelerates the reaction that produces the colour. Extension guidance on this is unusually blunt: do not iron over a deodorant mark. Once it has been baked in, a good deal of it never comes out.
Which produces an unfortunate sequence that plays out in a lot of households. Shirt yellows slightly. Owner bleaches it. Yellow deepens. Owner bleaches harder and irons it. Shirt is now permanently marked and structurally weaker than it was six months ago.
What actually works
Prevention is most of it, and it costs nothing.
Let antiperspirant dry completely before the shirt goes on, because most of the transfer happens when it is still wet. Use less than you think you need. If your shirts matter to you, an aluminium-free deodorant removes the mechanism entirely.
Don't leave a worn shirt sitting in a basket for four days in Indian heat. The longer the residue sits, the more of the reaction happens before you get anywhere near it.
For a mark that already exists, work on it before it sees heat. Undiluted dishwashing liquid rubbed into the area and left to sit, then laundered normally, is the method textile extension services recommend, and it works because the target is partly lipid. Oxygen bleach is safe on cotton where chlorine is not. For collar rings specifically, a degreasing agent applied directly and given time will lift most of it, since sebum is just oil.
And drying whites in sunlight does more good than most laundry products. Ultraviolet light breaks down the yellow compounds and does it without touching the fibre the way chlorine does. India has an abundance of the one bleaching agent that is both free and harmless.
The other failure: shirts that go sheer
Yellowing is chemistry. Transparency is mechanical, and it is where the cloth itself decides the outcome.
A shirt worn here gets washed after a single wearing, which is somewhere near 150 cycles a year. Every cycle abrades the surface slightly. Fibres work loose, break, and leave. The cloth thins, and a white shirt that has thinned goes translucent long before it develops a hole.
How fast this happens depends almost entirely on how the yarn was built. Cloth spun from short-staple cotton has an enormous number of fibre ends sitting on its surface, and each of those is something that can be rubbed loose and lost. Long-staple cotton has far fewer, so there is much less available to leave. Plied yarn helps for the same reason, since twisting two yarns together traps the loose ends between the strands rather than exposing them.
This is also why cheap shirts pill and fine ones do not. A pill is just surface fibre that worked loose and tangled into a ball instead of falling off. If there is nothing on the surface to work loose, nothing pills.
There is a corollary that is worth knowing when you are buying. A very high count shirt is thin to begin with, and it has less material to lose before it starts showing light through. A cloth built from two plied yarns at a moderate count has more substance and a smoother surface at the same time, and it is the reason that construction has survived in shirting for a century.
The short version
The yellow under your arms is aluminium and protein, not dirt. Bleach sets it. Heat sets it harder. Sunlight and a degreaser undo most of it if you get there before the iron does.
And the shirt that goes see-through in eighteen months is telling you something about the cotton it was made from, which was decided long before you bought it and cannot be fixed afterwards.
Sources
The mechanism by which aluminium salts in antiperspirants react with sweat proteins and lipids to form yellow, insoluble complexes bound to cotton is documented across textile extension guidance, dry-cleaning industry practice and consumer-science summaries. See for example The Stain Library, which collates university extension textiles guidance on deodorant stains, including the instruction not to apply heat or iron over such a mark.
On chlorine bleach setting rather than removing antiperspirant stains, and weakening cellulose in the process: the American Cleaning Institute's guidance against chlorine bleach on antiperspirant-stained fabrics is widely cited; see also DadMode's summary of the mechanism.
On apocrine sweat composition and the role of aluminium-based actives: Thompson Tee and Dermadry.
Fibre length, surface hairiness and pilling behaviour: Status & Prospects: Extra Long Staple Cotton Production in India, ICAR-CICR, published by the Cotton Association of India, February 2025. caionline.in