Orange or rust-colored marks on towels can be caused by minerals or bacteria in the water supply, especially in homes using well water. They may also result from a reaction between sunscreen residue and minerals such as iron or copper in hard water, which is why ordinary washing may not remove them.

Iron-related discoloration may appear even on freshly washed towels and can sometimes be accompanied by an unpleasant odor or orange buildup around faucets, sinks, or toilet tanks. These signs may point to an issue in the household water supply rather than a problem with the towels themselves.

Sunscreen-related stains are more likely to appear after swimming, beach trips, or other outdoor activities. Ingredients such as avobenzone can react with minerals in water, leaving noticeable orange marks on light-colored towels after contact with treated skin.

To treat mineral-based stains, soak towels in warm water mixed with citric acid or white vinegar, then wash them with an oxygen-based bleach. For sunscreen stains, apply dish soap to the affected area before washing in warm water with oxygen-based bleach, and allow towels to air-dry until the marks have fully disappeared.