Determining whether your young child has a food allergy can be a difficult thing to do.  It often takes some time for parents to even begin to suspect that their child may be experiencing an allergy.  To make the situation more complicated, many parents are not aware that their child while appearing to suffer from what they assume is an allergy may actually have what is called a food intolerance, also called a food reaction.   These conditions may sometimes appear similar but they are not.   

Allergic reactions
These conditions are quite different and are caused by different reactions within the body.
When the body has an allergic reaction what happens is the body is mistaking a food for a harmful agent of some sort.  It reacts because it thinks the food is a dangerous invader.  The reaction you see is caused by the body releasing antibodies that are called immunoglobulin E (IgE).  This IgE causes the body to release chemicals called histamines.  As the histamines are released, the body begins reacting by producing a variety of symptoms including itchy eyes, a runny nose, a skin rash and in severe cases even anaphylaxis.

Food Intolerance and Food reactions

What is different about either a food reaction or food intolerance is that they do not involve the immune system as in an allergy.  Also unique is that a food that causes such a reaction may be tolerated very easily at other times.  A good example of this commonly occurs with citrus fruits.  Infants may react to the high acidity of citrus and be intolerant to the fruit.  However the infant won’t react with an immune response but rather with a gastrointestinal or even dermatological response.  Infants below the age of one often experience rashes near the mouth or bottom, or they may have tummy cramps. 
When the child is older, it may have no reaction to citrus at all.

Lactose intolerance is another common example of food intolerance.  This is typically experienced by people who lack a specific enzyme that aides in the digestion of sugar (lactose) in dairy products. 

Identifying a potential allergic reaction

There are a number of signs to watch for that may indicate your baby is experiencing a possible allergic reaction or an intolerance to a food.  Your child may start vomiting or experiencing diarrhea.  They may have rashes on the skin or bottom.  Their face may begin swelling on the face or tongue area, or break out with hives.  They may have a runny nose.  They may experience breathing troubles.  Their throat may tighten or  appear almost closed.  They may show irritability or gassiness.  If any of these symptoms show up after the child eats a new food, they may evidence a potential allergic reaction or an intolerance to a specific food.   One good thing to remember is that with a food intolerance, the symptoms typically involve the intestines and some related reaction.

Allergies and the 4 day rule

One method that has been very helpful is to introduce a new food over a period of days.  This usually gives a more reliable indication of whether your child reacting negatively to the addition of a new food to their diet.  This is particularly advisable if any family members have a history of food allergies. 

In using the four day waiting rule it is important that you be introducing these new foods one at a time.  This prevents confusion of which new food might be causing a reaction.  If you suspect a reaction, it is easy to eliminate the food and watch your child for a few days.  This should give a good indication of a likely problem food for your child.  An additional precaution, if you are particularly concerned can be introducing a new food in the morning or early afternoon.  This would likely give you an opportunity to contact your pediatrician to discuss any apparent adverse reactions you observe while the doctor is reachable during normal office hours.