They are not nuts but truly seeds. There is lots of info on Wikipedia. They have been used in cooking as far back as King Tut. I have never heard of lots of people being allergic to them but I suppose anything is possible
Whatever they are, my sister is definitely allergic to sesame seeds and sesame oil. She also has allergies to eggs, chicken and nuts.
It is seeds ,the middle east use it to make hummos, tahini salad, and the halawa is made from the same thing.