The answer is a very long list of ingredients, that mostly do not do your body any favours at all.
Here is what is in the McDonalds Tartare Sauce :
-Modified corn starch
-Dried egg yolks
-Corn syrup solids
-Xanthan gum (415)
-Potassium sorbate (202)
When you purchase McDonalds products – you are actually voting with your dollar.
Are you really happy consuming all these ingredients?