Real mayonnaise doesn't contain any sugars and is a great low FODMAP food.
Check ingredients to be sure it doesn't contain and extras like onions or garlic.
It is a stable emulsion of oil, egg yolk, and an acid, either vinegar or lemon juice. There are many variants using additional flavorings. The proteins and lecithin in the egg yolk serve as emulsifiers in mayonnaise. The color of mayonnaise varies from near-white to pale yellow, and its texture from a light cream to a thick gel.
A typical formulation for commercially made mayonnaise (not low fat) can contain as much as 80% vegetable oil, usually soybean but sometimes olive oil. Water makes up about 7% to 8% and egg yolks about 6%. Some formulas use whole eggs instead of just yolks. The remaining ingredients include vinegar (4%), salt (1%), and sugar (1%).