There are two reasons that this can happen.
Carpet cleaned then spot returns.
As carpet dries water evaporates from the tips of the carpet yarns drawing some of the remaining moisture behind it.
The reason the spots return has to do with the mechanics of capillary action.
Do not scrub the area.
These returning spots can be as much of a surprise to your carpet cleaning professional as they are to you.
At other times the spots and stains come back after the passing of a few weeks.
Sometimes spots can reappear as soon as the carpet dries.
Now the remaining liquid will carry some of the spill back up to the carpet surface due to capillary action also called the wicking effect.
After cleaning a spot or stain from your carpet there are times where it will return just shortly after the carpet dries.
This is most often a result of wicking which will be discussed below.
Say you use a fair amount of spot cleaner to clean up your spill and finish by blotting up the tips of the carpet fiber.
When the carpet is cleaned it looks good.
How to make sure a spot does not come back after cleaning.
Vigorous scrubbing could damage your carpet or upholstery.
Using a white cloth or towel depending on the size of the stain gently rub the area back and forth or in a circular motion so the water based cleaning mixture covers the entire stain.
Either way it can be quite annoying to see spots and stains re emerge on a carpet you thought was just professionally cleaned.
Another common reason for returning spots after carpet cleaning is residue in the carpet.
So it may come as a surprise when some of the spots return.
When it dries the spots and traffic areas come back.
One originates below the carpet fibers in the backing or pad of the carpet.
The good news is that if a spot actually wicks back it can be removed.
Wicking is one of the most common result of returning spots.
Other times the spots come back after several weeks have passed.
These type of spots usually start out as a spill.
There are two primary causes of carpet re spotting.
Re soiling from various residues and soil wicking after carpet cleaning.
Returning spots after carpet cleaning a manufacturing issue.