The Stain Library

How to remove baby sick from swimwear

Published by The Stain Library. How we research our methods.

  • DifficultyEasy
  • OutlookUsually removable
  • MaterialSwimwear
  • Reviewed7 September 2026

The short answer

Rinse it by hand in cold water immediately, then hand wash with a little mild detergent and rinse again. Swimwear barely stains, because the fibres are smooth and non absorbent. UK retailers are explicit that swimwear should never be machine washed even once, never tumble dried, never ironed because the fabric disintegrates, and never bleached.

If it has just happened

Rinse it under a cold tap by hand within a minute or two. Nothing about swimwear holds a milk mark, so a prompt rinse is usually the entire treatment.

Avoid heat while treating the stain

Avoid adding heat while treating this stain. Follow the material's care instructions and the method below; heat may make a mark harder to remove or damage the material or its finish.

Test on a hidden area first

Use only a cleaner allowed by the material's care instructions. Test it on an inconspicuous area with the same material and finish, or a matching offcut. Let the test area dry and check for changes in colour, texture or finish before treating the visible mark.

Cleaning the mark is not the same as disinfecting

If the sickness came with a stomach bug rather than an ordinary posset, the surface may carry norovirus, which spreads easily and survives on hard surfaces. UK public health guidance is to wear gloves, avoid shaking contaminated laundry, wash affected laundry separately with normal powder at 60 C where the care label allows it, and disinfect compatible hard surfaces with a bleach based product afterwards. Do that after the stain work, not instead of it, and only where the material tolerates it.

Keep every kind of drying heat away until the mark has gone

Baby sick is mostly milk protein. Heat coagulates protein and locks it into the material, which is why a mark that would have washed out can become permanent after one hot wash, one pass with an iron, a hairdryer or a spell on a radiator. Cool or warm treatment, air drying, and a proper look in daylight before anything warm goes near it.

What you will need

  • Disposable gloves Sickness that came with a stomach bug is a hygiene job as well as a stain.
  • A spoon or blunt scraper For lifting solids off before any water is involved.
  • Cold running water Cold first, always. Heat sets milk protein into the fibre.
  • Biological laundry detergent What this is The enzymes break milk protein apart, which is exactly the job here.
  • A bowl or a sink for soaking Soaking is where most of the work happens on a synthetic.

Helpful but not essential

  • An oxygen based stain remover powder For white and colourfast items only, and only where the fibre allows it.

Fresh baby sick on swimwear

Cold water first, then enzymes. In that order, every time.

  1. Scrape the solids off

    A spoon, working inwards. Do this before any water, because wetting solids spreads them into a much larger mark.

  2. Rinse from the back under a cold tap

    Hold the fabric with the mark face down and run cold water through the back of it. That pushes the milk out the way it came in. Cold, because warm water starts to set the protein.

  3. Work in biological detergent and leave it

    Rub a little neat biological detergent into the damp mark with your fingers and give it fifteen minutes. The enzymes cut the milk protein into pieces small enough to rinse away, which is the whole mechanism.

  4. Wash cool and check before drying

    Hand wash only, in cold water with a little mild detergent, and dry flat in the shade. Retailers say not to machine wash swimwear even once.

  • How longFifteen minutes, plus the wash
  • RepeatingRinse until the water runs clear before washing.
  • Stop ifthe water runs clear and no residue is left in the weave

Dried baby sick on swimwear

Soaking does the work. Time replaces the heat you are not allowed to use.

  1. Flake the dried milk off

    Work the fabric between your fingers to crack the crust and brush the pieces away. Dried milk on a smooth synthetic sits on the surface and a good deal of it comes off dry.

  2. Soak in cool water with biological detergent

    Thirty minutes for a recent mark, several hours for an older one. The cleaning trade body's guidance for spit-up is exactly this: soak fresh marks for at least half an hour and older ones for several hours.

  3. Work the mark between your fingers

    Every so often, squeeze and rub the fabric gently against itself where the mark is, which lifts softened residue out of the weave.

  4. Rinse, wash cool, and inspect before drying

    Look at the fabric while it is wet and again once it is dry. If any shadow remains, soak it again rather than putting it in a dryer.

  • How longThirty minutes to several hours
  • RepeatingRepeat the soak rather than raising the temperature.
  • Stop ifthe mark has gone before the item goes anywhere near a dryer

Old or set in baby sick on swimwear

An old milk mark on a synthetic is usually a yellow stain from the fat rather than the protein.

  1. Overnight soak in biological detergent

    Cool water, a scoop of biological powder, and leave it. Long contact time is the only lever available once heat is ruled out, and it is a surprisingly effective one.

  2. Then an oxygen soak on white and colourfast items

    An oxygen based stain remover in cool water tackles the yellowing from milk fat that enzymes leave behind. Check the care label first, and test a hidden seam on anything coloured.

  3. Wash cool, and look at it dry

    Old marks look worse wet. Dry the item in the air and look at it in daylight before deciding whether it has worked.

  4. Then stop, before the dryer

    If it is not gone, a hot wash or a tumble dry will make it permanent. An item with a faint shadow is still usable. One that has been baked is not going to improve.

  • How longAn overnight soak
  • RepeatingTwo long soaks, then accept it.
  • Stop ifthe mark has gone, or two long soaks have left it unchanged

What not to use on swimwear

  • A hot wash, a tumble dryer, an iron or a radiator, while the mark is still there

    Baby sick is mostly milk protein and heat coagulates protein into the fibre. Every synthetic here is separately heat sensitive as well, so a hot treatment risks glazing or melting the fabric while it fixes the stain.

  • Rubbing hard at the mark with a brush

    Synthetic fibres are smooth, so residue lifts off with soaking rather than force. Hard rubbing raises fibre ends and produces a pilled patch that stays visible after the mark has gone.

  • Putting it in the wash and hoping

    A normal wash cycle is not long enough or cool enough to be relied on for milk protein, and if it fails the item comes out of the machine with the stain set. Pre-treat first, then wash.

  • Putting it in the washing machine, even once

    UK retailers give this instruction explicitly. The agitation and the spin cycle damage the elastane and distort the shaping, and a swimsuit is small enough to hand wash in a minute.

  • Chlorine bleach

    Chlorine resistant does not mean chlorine proof. Household bleach destroys the elastane, and the damage shows up as a slack garment rather than as a faded one.

  • Tumble drying or ironing it

    High temperatures make swimwear fabric disintegrate rather than simply crease. Air dry it flat in the shade.

White compared with coloured swimwear

Swimwear is usually a strong print or a dark solid colour and the dyes are chosen to survive chlorine and sunlight, so a cold rinse presents no colour risk at all. The thing to protect is the elastane, and both chlorine bleach and heat destroy it without changing the colour, so the damage is invisible until the garment goes slack.

If the mark is still there

There is rarely anything left to do. If a faint mark remains, a second cold hand wash with a little mild detergent will normally finish it.

What is worth doing properly is the drying. Lay it flat in the shade rather than hanging it in the sun, because sunlight degrades elastane and fades prints, and retailers suggest giving a swimsuit 24 hours between wears for the elastane to recover.

If a smell remains, rinse it again rather than reaching for anything stronger. Swimwear has no absorbency to hold a smell for long, and a persistent one usually means the garment was left rolled up wet, which is a different problem.

When to stop and call someone

There is no professional route for swimwear and dry cleaning is specifically inappropriate for it. If two cold hand washes have not dealt with a mark, or the fabric has gone slack or crisp, the swimsuit has reached the end of its life rather than needing a specialist.

Why baby sick behaves this way on swimwear

Swimwear is nylon or polyester with elastane, engineered to stretch and to survive a swimming pool.

It hardly stains

The fibres are smooth and non absorbent, so milk has almost nothing to bond to. This is one of the easier surfaces on the site for this stain.

The rules are about the elastane

The instruction not to machine wash a swimsuit even once is about the agitation and the spin, not the water. The instruction not to iron it is because high temperatures make the fabric disintegrate rather than merely mark it.

Chlorine resistant is not chlorine proof

Chlorine resistant fabric simply survives pool water longer. Household bleach is far more concentrated and destroys the elastane outright, so the fact that a swimsuit lives in chlorinated water is not a reason to think bleach is safe on it.

Sunlight ages it

Drying in direct sun degrades the elastane and fades the print, which is why shade is specified.

Sources

What we checked and when. Where a manufacturer instruction disagrees with anything here, follow the manufacturer.

  1. How to remove baby formula stains, Purex Stain Lab manufacturer

    Manufacturer guidance identifying breast milk, formula and baby spit-up as protein stains, explaining the role of enzymes, and warning that the mark should be checked before any drying heat because heat sets what remains.

    Checked 7 September 2026

  2. How to remove stains from baby clothes, Persil UK manufacturer

    UK manufacturer guidance to act quickly on formula, blot when immediate washing is impossible, rinse under cool water, soak for at least 15 minutes where the care label permits, pre-treat with detergent and then wash to the care label.

    Checked 7 September 2026

  3. A guide to newborn laundry, American Cleaning Institute trade body

    Cleaning trade body guide to pre-treat breast milk, formula or spit-up with an enzyme stain remover, soak fresh marks for at least 30 minutes and older marks for several hours, launder, and keep stained items out of the dryer until the mark has gone.

    Checked 7 September 2026

  4. How to clean polyester and synthetics, Woolite manufacturer

    Detergent manufacturer guidance that polyester is washed, dried and ironed at low to medium heat only because excessive heat can melt the fibres, that air drying is preferred to machine drying, that nylon is washed in cool water on a gentle cycle because repeated machine washing causes discolouration and loss of shape, and that acrylic knits are laid flat or dried at low temperature to keep their shape.

    Checked 7 September 2026

  5. Norovirus: what to do and how to stop the spread, UK Health Security Agency authority

    UK public health guidance establishing that illness related vomit can carry norovirus, that contaminated laundry should be washed with normal powder at 60 C where the care label permits, and that compatible hard surfaces should be disinfected with a bleach based product.

    Checked 7 September 2026