Sunscreen
Two stains in one bottle: an oily film, and a UV filter that forms a coloured complex with the iron in your water. The second one is why the mark comes out orange.
In detail
Sunscreen is the clearest example here of a stain that is not one thing. The base is an emulsion of oils and emollients, and that part behaves like any other greasy soil. The part causing the trouble people search for is the UV filter, and specifically avobenzone. Avobenzone carries a 1,3-diketone group, and a technical account from an institutional cleaning-chemistry company states what that means in a washing machine: the group forms strong metal complexes, and where the water is iron-rich the sunscreen actives combine with the iron to form highly coloured complexes. That is the mechanism behind the orange marks readers describe, and it explains why the stain often was NOT visible before the wash — the complex forms during washing, not on the beach — and why it looks like rust without rust being present. Two consequences matter more than the mechanism. The same source records that these stains are SET by high-pH washing and by chlorine bleach, and that ordinary detergent, booster and bleach combinations have failed to remove them. The two instincts a reader is most likely to act on are the two documented to make the mark permanent.
Why
- Sunscreen is explained by Chelation
The catalogue already models chelation as the thing that binds metal ions in cleaning. This is the same chemistry working against the reader: a UV filter chelating iron, and the complex is coloured.
- Sunscreen is explained by Water hardness
The unusual case: hard water normally leaves a deposit you can see. Here it supplies the iron that turns an invisible residue into an orange stain.
Hacks and claims involving this
- Orange sunscreen marks are rust Does not work
Sources for this page
Sources
Cleaning composition and method for removal of sunscreen stains, US patent US9222058B2
Ecolab USA Inc., granted by the United States Patent and Trademark Office, 2015 · Manufacturer documentation
Relied on for: That avobenzone's 1,3-diketone moiety is known to form strong metal complexes, that sunscreen actives combine with iron in the water to form highly coloured complexes and iron-rich water gives more highly coloured stains, that such stains appear as yellow patches after washing at high pH, and that they are set by alkaline conditions and by chlorine bleach. (states this directly)
Verification: a person has read the passage relied on.
Read on — The background and description. Inventors: Dawn N. Lock, Stephan M. Hubig, Kim R. Smith, Joshua A. Ackerman. Supports the claim as stated. The avobenzone-and-iron hypothesis carried since Sprint 17 is supported, and by a technical source rather than by the blogs that were repeating it. Two things the blogs do not say came with it and are more actionable than the mechanism itself: high-pH washing and chlorine bleach SET the stain rather than removing it, and ordinary detergent plus bleach is documented as unsuccessful. Those are now the operative facts on the sunscreen record.
Sunscreen stains, one of the hidden costs in laundries
Christeyns, 2023 · Credible secondary source
Relied on for: That avobenzone is an oil-soluble UV filter present in most sunscreens which reacts with iron minerals in the water to produce rust-coloured staining, that the stains are yellow-orange, that iron-rich regions see more of it, and that synthetic fabrics are more susceptible than cotton. (states this directly)
Verification: a person has read the passage relied on.
Read on — The description of the staining mechanism and the recommended treatment. Supports the claim as stated.
Last reviewed by a person on .