So how can you tell if you've got bad breath, as opposed to paranoia? We British are far too reticent to be honest with friends, family or foe, and private healthcare, sensing a gap in the market, has actually set up "fresh breath centres" in some cities, where you blow in a halimeter that measures stinky breath chemicals such as hydrogen sulphide.
If you never clean your teeth properly, you're likely to have bad breath caused by the rotting bacteria in plaque. As my dentist puts it, only floss the teeth you want to keep. If your gums are sore and swollen, and bleed easily on contact, you've got gum disease and breath to match. Stick your tongue out full, lick your wrist and smell it a few seconds later. If it's cheesy, so is your mouth.
Still not convinced? A BreathAlert device from a pharmacy grades your breath from none to strong (batteries not included). Failing that, ask your dentist. He or she has a financial incentive to give it to you straight.
So, what can be done? Persistent bad breath needs a visit to the dentist and a resolution to brush and floss regularly for life. This is far more effective than masking the smell with mints or parsley. Sometimes bad breath is caused by a steady drip of snot at the back of the throat, which may be caused by an allergy or infection and clears after treatment. And if a kid in your class has really stinky breath, think tonsils or plastic bead stuck up nose. Either way, refer them to the surgery.
A tongue cleaner scrapes gubbins off your tongue like a garden hoe but most people have bad breath because no one ever taught them to clean their teeth properly. See www.embarrassingproblems.co.ukbreath.htm
Phil Hammond is a GP and broadcaster and chair of governors of a primary school. His new book, Medicine Balls, was published by Black and White Publishing on November 1 (pound;9.99, paperback).