Acid rain is rain with a lower than normal pH, caused by emissions of sulfur dioxide (SO2) and nitric oxides (NOx), typically from factories, though there are natural sources.[note 1] This is quite bad for aquatic animals, plants, and buildings. Government regulations have had positive results on curbing acid rain. The term "acid rain" is bit misleading as all rain is slightly acidic. Most people think of "GAH, MY FLESH IS MELTING!" when they think of acid rather than toxicity to aquatic life if allowed to build up in higher concentrations. Human health effects are also indirect. You won't actually melt if you stand out in acid rain, nor will you suffer effects from the rain touching your skin; the damage actually comes from breathing in the sulfur and nitric oxides.[1]