The lower the LD 50 value, the more toxic the substance. Diazinon, then, is more toxic than whole neem oil. In this case, the organic pesticide is more than three times more toxic than the synthetic one. LD 50 also applies to dermal exposures as well. In this case, exposure means contact with the skin of the test animal.
Skin usually requires more exposure to a substance in order to achieve the same result.
The dermal exposure numbers, however, do not account for the more vulnerable portions of the human body. On a man, for example, the forearm, palm and ball of the foot absorb a chemical at a slower rate, while the armpit and scrotum absorb up to 12 times more quickly . Not all exposures come in the form of ingestion or skin contact. If your neighbor sprays a chemical, you can be exposed to its effects by inhaling the compounds. Unfortunately, data on lethal concentrations is the least known, least tested and least regulated.