It was often recommended for making the various homemade pest control recipes and reportedly is not harmful to the plants when mixed in the proper proportions as modern detergents can be.

However naptha does have some negative side-effects of its own - petroleum-based hydrocarbon and known carcinogenic.

Dave

''Carcinogenicity: None of the ingredients in this product are listed as carcinogens by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP) or the Occupational Safety and Health Administration (OSHA). ''

Fels-Naptha Heavy Duty Laundry Bar

I've used it for years to spot clothing. It just seems those sprays and other spot removers don't work well. I wet the bar, wet the spot, rub the bar in and scrub a bit by rubbing together with my hands. Let sit a few minutes, then put in the washing machine. Might not be good to let it sit too long. Spots almost always come out.

I just started using a Fels Naptha based spray for my aphid problem on veggie plants so I really hope this isn't accurate.

I did google around and found that Naptha is NOT the same as Napthalene (moth balls) which IS a carcinogen. However Wikipedia states that some forms of Naptha MAY contain carcingogens. The wikipedia for Fels Naptha states that it only really contains some irritants.

I could not find any source outside of random forums stating that Fels Naptha specifically contains carcinogens.