As searing hot days continue this summer, heatstroke and heat exhaustion have sent record numbers of people to hospitals.

Drink lots of water, stay indoors and use air-conditioning, doctors say. But if you have irritated eyes or a sore throat, or feel dizzy or nauseated after being outside on a hot, windless day, you may be suffering from something totally different.

Chances are you have been exposed to photochemical smog, a form of air pollution that traces its history to the 1970s when Japan's rapid industrial growth was not only driving an economic boom but also aggravating pollution.