Sweeteners are sugar substitutes that have a high sweetening power. The difference with sugar is that they do not provide a single calorie (non-caloric sweeteners), much less than sugar. However, its sweetening power is much greater than that of sugar.
The most typical sweeteners are: saccharin, cyclamate, acesulfame K, aspartame, sucralose, xylitol, sorbitol or stevia.
Many times you will find them "hidden" on product labels under the name "E-number".
Sweeteners are safe and are authorized by the Food Safety Authority (EFSA), if the Acceptable Daily Intake is followed (you would have to carry kilos of sweetener so that they were not).
People with diabetes, who have to control their sugar intake, can find a solution in sweeteners to sweeten their coffee or tea.