Carpet shampoo is a specially-formulated liquid detergent compound used to clean carpets and rugs. Carpet shampoo is often used in conjunction with a rotary-style carpet cleaning machine or a cylindrical model which uses compressed air to generate foam before agitation. The general idea of using carpet shampoo is to create a thick foam which will attract and suspend dirt particles scrubbed out of the carpet pile. Once this dirty foam has dried, the residue can be vacuumed away.

A good carpet shampoo must be able to generate a considerable amount of long-lasting foam to be most effective. This means the use of ingredients similar to those found in hair shampoos. A chemical called sodium lauryl sulfate gives carpet shampoo its foamy quality, while dirt removers called anionic detergents provide cleaning power. Because dirt particles actually form an electrostatic bond with carpet fibers, anionic agents are used to break that bond and provide a more 'attractive' alternative.

Because the carpet cleaning machine uses strong brushes to agitate the foam, a good carpet shampoo must also have a lubricating quality to protect the carpet from tangles and distress. A carpet shampoo used in conjunction with a wet extraction machine should also contain water softeners.

The use of carpet shampoo is not universally embraced by the carpet care industry, however. One major problem with a detergent-style cleaner is the possibility of resoiling. The sticky carpet shampoo residue left behind after a cleaning session may actually attract more dirt. Professional carpet and rug cleaners may use a much lower concentration of carpet shampoo, if they use it at all. Some cleaning experts suggest that pure hot water does an effective job of cleaning without the harsh chemical odors or potential for moisture damage.

Some eco-friendly companies do produce a more organic version of carpet shampoo. Chemical deodorizers and detergents have been replaced with herbal concentrates and natural surfactant cleansers. Consumer-friendly carpet shampoo treatments are also available in the cleaning supplies aisle at grocery stores and retail outlets. These carpet and rug cleaning sprays eliminate the need for rented commercial rug machines. Be sure to vacuum thoroughly before and after application, and allow the carpet shampoo to dry completely for best results.

One controversial element of a carpet shampoo system is called an optical brightener. Because the actual detergent properties of some carpet shampoo brands are decidedly weak, manufacturers may add a special dye to the formula. The dye, called an optical brightener, creates little more than an optical illusion. Carpet fibers receiving this dye convert ultraviolet light to visible light, creating a temporary brightening effect. Over time, the fibers become permanently yellowed, with little hope of restoration. Professionals suggest that consumers avoid any carpet shampoo which features optical brighteners.