Which Carpet Cleaning Method is Healthiest?
By Doug “The Rugman” Watson

I’d like to talk about three common methods for cleaning carpet: carpet shampooing and the hot water extraction method.

Shampoo Method
   
The theory in the shampoo method is to generate a lot of foam in the carpet, allow this foam to dry, have the resulting residue attract the soil, and vacuum up the residue and soil the next day.  Carpet shampoo products must have the following characteristics, which dictate their ingredients:

Very high foam levels to reduce wetting.
Very stable foam.
High lubricity to reduce damage to the carpet fibers from the brushes.
Dry to a non-sticky residue.
   
Therefore, a carpet shampoo must contain a very foamy chemical. The most common ingredient is sodium lauryl sulfate or one of its relatives. Sometime when you're taking a shower or bath, look at the ingredient statement on your hair shampoo bottle. It will say "Contains Sodium Lauryl Sulfate" or some similar wording. Sodium Lauryl Sulfate and its relatives exhibit a very high and very stable foam and are only fair detergents. The problem is that they dry to a soft, sticky residue, which will cause resoiling.

Because of the resoiling problem, carpet shampoos will frequently also have an anti-resoiling additive such as a resin to reduce this resoiling tendency.  Because shampoos are actually very poor detergents and simply bury the dirt, they frequently also contain high levels of optical brighteners which take invisible ultraviolet light and convert it to visible light, thus making the carpet appear cleaner and brighter than it really is, for a while. It will eventually give the carpet a yellow cast and the yellow cannot be removed.

Dry Cleaning

A dry absorbent compound (containing small amounts of water, detergent, and solvent,) is sprinkled over carpet or worked into the carpet with a machine. This purpose of this cleaner is to attract and absorb soil. Mechanical agitation from a brush works the cleaner through the carpet.

The theory is that the liquids dissolve the soil and this soil/detergent/solvent mixture is absorbed into the carrier and is then vacuumed.  With the extremely fine powder types of mixtures, indoor air quality can be reduced. If a white powder starts appearing on shoes and cuffs of pants, too much was used and it was not thoroughly vacuumed up.

Hot Water Extraction
   
This method is often call "Hot Water Extraction" and is the cleaning method nearly all carpet manufacturers and carpet fiber producers recommend.
   
This is the only cleaning method classified as "deep cleaning". All the others are considered "light surface cleaning" because they are incapable of removing soil deep in the pile. Also, all other methods leave large amounts of cleaning agent in the carpet after cleaning.
   
This process consists of spraying a solution of water and detergent into the carpet pile and recovering the water and soil with a powerful vacuum.
   
From a health standpoint, the truck-mounted extraction system is preferred because the dirty air and humidity are exhausted outside rather than circulated around the house. Additionally, truck-mounted systems are ten times more powerful than portable units and do a much better cleaning job and get the carpet dry more quickly.

General Comments
   
The choice of the proper cleaning system is extremely important. Some systems leave residues which promote re-soiling and defeat the whole purpose of cleaning. Some methods actually damage the carpet fibers and shorten the life of the carpet.

Carpet in a typical household should be professionally cleaned every 6 to 12 months depending upon the number of residents, amount and type of activity, and whether the carpet is light or dark color.
   
The maintenance brochure published by the world's largest carpet manufacturer, Shaw Industries, recommends professional cleaning over “Do-It-Yourself” because of the potential problems that can occur from using rental equipment - such as yellowing, over wetting, fiber tip damage, severe resoiling, overuse of detergents, etc.