Something unexpected and in fact disappointing can happen when our carpet is cleaned. When the carpet was cleaned at first everything looked okay, but after it was dry stains that had appeared to have been removed, reappear.
This is actually a fairly common situation, also referred to as wicking stains, and is caused by staining matter from a previous spillage having worked its way down to and dried at the base of the carpet pile . So when the carpet was cleaned, the tips of the carpet fibers were made clean but foreign material remained hidden further down. However, this hidden foreign material was made wet and in the drying and evaporation process wicked up to the surface of the carpet to reappear once again as the stain!
A second cleaning treatment should remove the last of it. It can also usually be removed by moistening the stain with a light mist and then blotting with clean absorbent toweling. If you need a second stronger treatment you can apply a general cleaner (such as liquid dish soap 1 part to 30 parts water) and blot up. Rinse after with clean water.
A good trick to help guarantee to the removal this reappearing stain is to take advantage of the wicking or evaporating process that the stain itself used in the first place. After having wet down the stained area, cover the stain with 1/2 inch of baking soda or powder. Let it dry overnight. Vacuum off in the morning. Utilizing the process of evaporation in removing these water based stains, takes more time, but can be just as effective as professional carpet cleaners using their supply of cleaning agents.