This is an article that explains a very common problem we see in homes called filtration soil. Filtration soil is the dark line that can show up on the edges of your carpet, normally about a half inch away from the wall going all the way over to the wall.
How to prevent filtration soil buildup
The best way to help prevent this from being a problem is to vacuum the edges of the carpet with the attachment of your vacuum. The vacuum is not going to get all the way over to the baseboard during regular vacuuming. If you look at the bottom of you vacuum you will see what I mean. This may only show on one wall in a room, this is normally due to the air flow of the room. Professional carpet cleaning may be needed to resolve this issue after it starts.
Filtration soil article
This article was sent from The Carpet and Rug Institute and gives a very good explanation for this issue. When we see it in a home or business we will do everything we can to remove as much as possible, but we normally can’t remove it completely. The other way we can help is to re-stretch the carpet so the area that is discolored is no longer visible. When doing this we can tuck the soiled area under the baseboard. Most carpet that has been down long enough to develop this problem has enough slack in it to be stretched an inch or two.
You can contact us if you have any questions.