Anyone who has visited a dentist has been told that eating excessive amounts of sweets risks harming the teeth. This is because sweets lower pH levels in the mouth to dangerous levels.

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When the pH level in the mouth is kept above 5.5, acidity is such that teeth are unlikely to be in danger of decay. Sweet foods, however, cause pH in the mouth to drop for a time, and the longer pH levels remain below 5.5, the greater the opportunity for decay to occur.

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By comparing fruit sugar, cane sugar and honey, which are all common ingredients of sweet foods, we find that cane sugar lowers pH levels for the longest period, thus producing the greatest risk of the three. Approximately five minutes aftfter consuming cane sugar, pH levels drop to as little as pH 3.5. They then begin to rise slowly, but do not rise above pH 5.5 until at least 30 minutes have elapsed. By contrast, fruit sugar, which causes the mouth's acidity to fall to just above pH 4, poses a danger for a shorter period: tooth decay is unlikely 20 minutes after consumption. Honey appears an even less risky substance. Though acidity falls to about pH 4.75 within five minutes of consumption, it returns to above pH 5.5 in under fifteen minutes.

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The implications, then, are that people who insist on eating sweet foods should be aware of the ingredients, and that fruit sugar or honey appear preferable to cane sugar.

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