I've posted about this in the past, but thought it would bear repeating.
My sister may have sensitized her oldest son to peanuts during her
pregnancy; she ate a lot of peanut butter during her last trimester. We
knew the baby was allergic all along bec. of his rough skin, but
thankfully he was fully breastfed for a long time and when solids were
introduced before one year, he was still kept away from eggs, dairy, and
citrus. When he was fourteen months old he got a taste of peanut butter
and ended up in the hospital with facial swelling. He was treated with
adrenalin and released. Subsequently we found that if another child ate
peanut butter in the same room he would have mild facial swelling;
cottage cheese landed on him during a "food fight" at school and he
developed blistery hives on the spot. and on and on....This child is
allergic to dairy, soy, fish, nuts, beans. Imagine if he hadn't been
breastfed....
Only the boys in the family have food sensitivities; but reactions have
been less severe bec. my sister has avoided  giving solids longer and
longer, and certainly avoiding those listed above, including not eating
peanuts while pregnant! So that her youngest son, who still breastfeeds
a lot at age 22 months, has beautiful skin, and a pleasant disposition!
Pearl Shifer, IBCLC