So what is the difference between an allergy or an intolerance?
An allergy is where the immune system generates an antibody to a substance.  These antibodies are known as immunoglobulins (Ig) and can be seen in the blood. There are different types of immunoglobulins:
IgE  These are immediate allergies where you get a reaction within 15 mins to 2 hours. The most severe form of reaction is Anaphylaxis. This can manifest in breathing difficulties, itching, rash, vomiting.  In the worst case lead to death, which is why many people with severe allergies will carry an EpiPen® an emergency treatment for anaphylaxis.
Less severe reactions include for example hayfever and hives.
IgG  These are delayed allergies and may take hours or days to manifest. It is harder for people to work out what may be causing their reactions as nothing happens immediately. Intolerances  These do not involve the immune system making antibodies, so you can’t see them in blood tests. They occur when the digestive system is unable to process food. This can be due to lack of an enzyme required to break it down.  E.g. lactose intolerance due to lack of lactase. Can also be lack of pancreatic enzymes or HCl. (stomach acid)

What kind of reaction will I get as a result of an allergy? 
The immunoglobulin (Ig) that is produced as a reaction to an environmental (e.g.pollen) or food (e.g. peanuts) irritant attach themselves to cells in our body called Mast Cells.  These cells are full of histamines, which are chemicals that cause the inflammatory response and our allergy reactions. 
So now you can see why people with allergies take anti-histamines, to block the production of histamine.  The reaction of a person to an allergen depends on where the mast cells are residing. For example:
·     Mast cells in the skin e.g. eczema, hives.
·     Mast cells of the digestive tissue e.g. gastric disturbances

What could be potential signs that you have an allergy or intolerance?

·     Skin conditions - eczema, psoriasis, hives, itching
·     Digestive issues - gas, bloating, diarrhea, constipation, reflux, heartburn, pain, IBD
·     Respiratory - asthma, cough, sneezing, blocked nose, frequent ear infections,
·     Eye - watering, red and itchy, dark circles under the eyes
·     Headaches
·     Fatigue, sleep issues
·     Other - blood sugar imbalances, autoimmune conditions, ADHD, autism, mental illness
·     Respiratory - asthma, cough, sneezing, blocked nose, frequent ear infections,
·     Food allergies - dairy, gluten, eggs, shell fish, nuts, additives
·     Contact allergies - nickel, perfumes, sprays, chemicals, pets
·     Airborne allergens - dust mites, pollen, moulds, fumes
·     Drugs - penicillin, aspirin, sulphur drugs
·     Chemicals - cosmetics, washing powders