Consumer-caused stains are also a big problem. This kind of unknown stain is caused by the consumer spilling a substance on the garment that may not be visible before washing. Common invisible stain leavers are soft drinks, cocktails, corn syrup, fruit juices and honey. When the stain dries into the fabric it may be undetectable, but if it is left in the garment may oxidize into a yellow stain. The additional heat from the laundering process increases this oxidation and sets the stain.
Items left in pockets are often the culprit of difficult, unknown stains.
Of course, checking items before laundering is crucial. If however, an item such as a crayon or lipstick escapes the check, the dryer drum may be stained. These drum stains must be cleaned before they stain other garments. This should be done by using a spray cleaner, a laundry pretreat product, or a mildly abrasive cleanser. After the drum, has been cleaned, one should tumble a load of wet old rags, or towels on regular temperature for at least 20 minutes.