1. Field of the Invention
The invention relates to cleaning compositions containing a major amount of soap and a mildness improving component to protect skin against surfactant damage.
2. The Prior Art
Soap is mankind's oldest surfactant. Although soap is efficient at cleaning, it requires formulation to overcome many physical property defects. Additives have been discovered which improve soap's lather, fragrance, visual appeal and other aesthetic properties.
More recently, attention has been drawn to the harshness problem of soap toward skin. Eighteen well-known toilet soaps were evaluated by Frosch & Kligman, "J. Amer. Acad. Derm.", pp. 35 (1979). Great differences were noted in their effect upon skin. Most had an appreciable irritancy. The study revealed that substantial replacement of soap with an alternative detergent such as acyl fatty isethionate would provide a more skin compatible system. Unfortunately, this alternative is expensive. Cheaper solutions to the harshness problem would be desirable.
Reports of blending soap with acyl fatty isethionates, presumably to lower costs, have been numerous. U.S. Pat. No. 2,894,912 (Geitz) extols the virtues of toilet bars containing from 30 to 70% acyl fatty isethionate and 2.5 to 25% soap. In U.S. Pat. No. 4,260,507 (Barrett), a composition with major amounts of soap, 60-97%, was combined with minor amounts, 3-40%, acyl fatty isethionate. These toilet bars were claimed to have exceptional lathering properties.
Acyl fatty isethionate is prepared by direct esterification of C.sub.12 -C.sub.25 fatty acid with the alkali metal salt of isethionic acid (known also as hydroxyethane sulfonic acid). Unesterified alkali metal isethionate itself has been reported as a toilet bar processing aid in U.S. Pat. No. 4,180,470 (Tokosh et al). Alkali metal isethionates, however, have never been reported as mildness improvers nor their use suggested in formulations where soap is present in greater amount than 25 wt. % of the total composition.
It is an object of this invention to provide a low cost cleaning composition containing major amounts of soap but substantially milder to skin than pure soap.
Another object of this invention is to provide a method for protecting skin against damage from contact with soap or any other surfactant.