I'm finding that organic foods and whole foods are the way to go. If it isn't natual or didn't come from the earth the way nature intended, keep away. The more additives, preservative and processing, regardless of whether or not the allergen is present (citric acid in our case), the more likely it is to affect the immune system.

My daughter is allergic to Citric Acid and I also have an allergy / intolerance to MSG, sulphites, dairy and some fruits. Citric acid is naturally found in citrus fruits (lemons, oranges, limes), most berries, majority of fruits except watermelons, pears, apples, grapes and low levels in bananas.
The worst thing is it's a persevative in everything from soups, sauces, conserves, sweets, juices, soaps, bodywash, sunscreen, chips, crisps, as a culture in some chesses, normally the cheaper processed ones, as well as ice-cream... you name it.
I've become very aware of the foods and products so if in doubt I avoid. I make 99.9% of meals, I send in her snacks for creche as it is very difficult for them to know the extensive list of products that have citric acid. Planning is key. Make time to read the ingredient list, do meal plans for your week. If you are making a dinner, make a batch so you have 2 or 3 portions in your freezer.

Sometimes I feel bad when I say "no she can't have that" so to prevent my daughter from feeling left out or deprived :-) when someone offers her a food she can't have I carry organic oatie bars with me so she can have these instead, As an emergency snack in Grandparents house I always keep a pack of organic vanilla yoghurts in the fridge.

Planning is key.

In my house I have the egg allergy. My Mom is on dialysis and has to have lots of protein, which means lots of eggs. I have learned to separate my eating utensils, plates and cookware from hers, because I have had mild reactions when using things that she had cooked/ used eggs. And I wash mine separately. Separation is my secret!

My son is allergic to wheat, all grains and eggs just to name a few. I substitute Corn Starch for flour and Apple sauce for the eggs. I make most of his food from scratch because even though it says the item is Gluten free it may still include eggs as well as grains.

Most everything at our house is made from scratch, and I make one meal for the whole family. I've posted some of our favorite allergy-friendly recipes at www.allergybitesblog.com

Olive oil is a good substitute for butter in some pasta dishes. Also, I assemble the allergy dish first bc for example, my granddaughter is very allergic to dairy and eggs, among other things. She likes lasagna and enchilladas so I would assemble hers first, without cheese then make the pan for the family with cheese. I set hers to the side. By making hers first and setting it aside I can relax, not having to worry about cross contamination.