Hi -

My understanding, from our own allergist, is that if a baby is having
allergic reactions to a food, you should *completely* eliminate that food
from his diet, even trace amounts.  The reasons are that:

1.  You don't want him to become even more sensitive to the allergen(s),
2.  You don't know which way his reactions are going.  Ie, they could get
more severe.  So you don't want to risk needing to call 9-1-1 because a
reaction prevents him from breathing.
3.  With a baby, it's not always possible to tell if he's having a very
mild reaction ... but *any* reaction can lead to a severe one.

It IS a pain dealing with allergen-free foods.  But there are a number of
resources on the web that can help you figure out the shopping, the cooking,
etc.  You do NOT have to cook separately for the baby, by the way!  His
particular allergens will force you to be a bit more creative, but your
whole family can eat a lot of what he eats and be the healthier for it.  And
psychologically, it's probably better for him not to feel "different" at home
due to eating special foods.  (Out of the home is a different issues, of
course.)

DO get hooked up with an allergist who deals with babies.  Not all allergists
do; many won't deal with children under 2 years of age.  But the ones who
DO deal with babies will be able to offer you advice, resources, and an
epi-pen for emergencies.

I hope this helps!
--Beth Kevles
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  http://web.mit.edu/kevles/www/nomilk.html -- a page for the milk-allergic