Topically (touching your skin) it is lethal for insects (critters with an exoskeleton) but generally safe for mammals. 5 grams eaten per 20 kilograms (~44lbs) of body weight can be lethal. So, 5 grams eaten could kill a 44 pound child. So, use it on your nail, and keep the bottle put away out of reach of children, like every other medicine, and it should be fine.