Fels-Naptha is a bar-type laundry soap sold in many discount and grocery stores, such as Wal-Mart or hardware stores such as Ace Hardware, as well as by online retailers. Stores usually stock this soap in the laundry aisle and not with hand or shower soaps.
Fels-Naptha is useful in removing many oil-based stains, such as chocolate, baby formula, makeup and perspiration stains, according to About.com. The user pretreats these stains by rubbing the moistened bar onto the fabric before placing the article in a normal laundry cycle.
Several recipes for homemade laundry soap use Fels-Naptha as an ingredient. Generally, these recipes call for grating the bar and adding the soap to other ingredients.
Early formulas for Fels-Naptha included Stoddard solvent, known as solvent naptha or mineral spirits, a substitute for turpentine also used by paint manufacturers. Dry cleaners once used this solvent in their cleaning processes. Wikipedia says the current Fels-Naptha formula has eliminated this skin and eye irritant, although the manufacturer still warns users that the product causes eye irritation and irritates the skin with prolonged contact.
Fels-Naptha helps to remove the oily residue of plants, such as poison ivy, that cause contact dermatitis. Washing these oils away before skin becomes inflamed eliminates the toxin. The product also helps to remove the plant oils from clothing that has contacted the irritant.