At times, water soaking into the backing can cause chemical reaction
with dyes in cellulosic fibers in the backing and these rise up to the
surface through the pile fabrics. This can occur after wet cleaning or
deep spills, specially under conditions of slow drying.
This problem is very acute with carpets using cellulosic fibers like
jute, cotton, sisal and wool in their backing. With time, jute backing
deteriorates giving rise to brown or red pigments called 'lignin' which
wick upto the surface of the pile fibers. (One of the first things to
be checked for is whether your carpet does have jute in it's backing:
most carpets made since 1980 don't use jute backing.)
A professional cleaner should be consulted to correct these stains but,
be prepared, the damage to the carpet may be irreversible. To prevent
these stains, IMMEDIATELY clean up all spills and remove all stains at
the earliest possible stage. Also speed up the drying time of your carpet
after cleaning by opening doors and windows. if possible, or using dehumidifiers
and other equipment that accelerates the drying process. Every precaution
must be taken because these stains, though usually reversible at first,
can become permanent if not treated timely.