One of the most common causes of a clogged bathroom drain is hair, and the thought of pulling out clumps of tangled locks makes most people run for the Drain-O. But common drain cleaners pack a toxic punch. They contain sodium hydroxide and sodium hypochlorite, which can cause permanent damage to skin and eyes on contact, and the vapors can burn lungs. Many also contain dimethyl benzyl ammonium chloride, a severe eye and skin irritant, and dichlorodifluoromethane (uh, what?), a neurotoxic eye irritant.