According to the Food Allergy Research & Education group FARE, an estimated 32 million people in the U.S. have food allergies, including 1 in 13 children.  Because allergic reactions to foods can be life-altering and potentially life-threatening, it’s crucial that the many signs of food allergies be known and their underlying causes well-understood. It’s also important that signs of food allergies not be confused with food sensitivity symptoms — the unpleasant physical reactions triggered by the digestive system’s inability to fully break down and absorb certain foods or their components.
A food allergy is an immune system response triggered when the body mistakes a harmless ingredient in food — usually a protein — as an invader (antigen) and overreacts by creating an army of antibodies to fight it.  These antibodies travel to cells that release powerful chemicals called histamines. 
The allergy symptoms one experiences depend on where in the body the histamine is released:
In addition to these mild-to-moderate signs of food allergies, other more severe symptoms can include:
Severe symptoms, alone or combined with milder symptoms, may be signs of anaphylaxis — a life-threatening condition requiring immediate treatment. Foods that most commonly trigger one or more of these allergic reactions include shellfish, nuts, fish, eggs, peanuts, and milk. 
Although they mimic many of the food allergy symptoms, food sensitivity symptoms are a response from the digestive system rather than from the immune system. Food sensitivity symptoms occur when a person’s digestive system is unable to properly break down and absorb certain foods or food components, often due to a deficiency of digestive enzymes.
Sensitivity to lactose, which is found in milk and other dairy products, is the most common food sensitivity and is caused by a deficiency of the enzyme lactase.
Food sensitivity symptoms can include:
While people with food allergies are generally advised to avoid the offending foods completely, those with food intolerances may not experience symptoms unless they eat a large portion of the food or eat the food frequently.
As you can see, sometimes it’s difficult to distinguish between the two but note the signs and symptoms listed above. If you still have questions, it’s best to seek out the advice of an allergist, who can test you for food allergies. If you test negative, then you know it’s likely a food sensitivity instead. Once you have determined it is not a food allergy, you can seek the advice of a dietitian or nutritionist who specialized in food sensitivity and GI issues to adapt your diet appropriately.
You may be surprised to learn that some vitamin pills (mostly tablets) can also exacerbate food sensitivities. Vitamin tablets typically contain hard “sand”-like particles that are too large to absorb. These large particles may be scratching the lining of the gut, causing inflammation that leads to food sensitivities symptoms. That’s why it’s a good practice to seek out pill-free vitamins in liquid form, or in gel form, like Healthycell’s Bioactive Multi that uses new MICROGEL™ technology. This new delivery technology uses a prebiotic gel matrix to deliver a broad spectrum of extremely small, dissolvable nutrient particles in highly bioavailable forms to make it easier for your body to absorb the nutrients it needs without irritating the gut.