The primary difference between an allergy and a sensitivity is that an allergy is characterized by an immune system reaction to a substance, while a sensitivity involves no immune response. Both, however, can be quite serious, as can intolerances, and a range of symptoms can be caused by allergies, sensitivities, and intolerances. For this reason, it is a good idea to see a doctor about symptoms which appear to be linked to exposure to certain substances, to figure out precisely what is going on.
In the case of an allergy, the immune system learns to attack a particular substance for an unknown reason. In order for an allergic response to develop, someone must be exposed to the substance at least once before the response will manifest. A classic example of an allergic reaction is to peanuts, in which the immune system regards peanuts as harmful, and goes into overdrive when someone consumes peanuts or is exposed to peanut products.
Some common symptoms linked with allergic reactions are dermatological symptoms like eczema and hives, respiratory problems, anaphylaxis, rhinitis, and shock. These symptoms may emerge immediately, or within a few hours, depending on the type of allergy and the severity of the immune system response.
A sensitivity involves no immune system response, but it can still yield a multiplicity of symptoms, ranging from issues in the digestive tract to neurological problems. Some of the issues associated with sensitivities can become life threatening, especially if someone is exposed to a substance repeatedly, which is why it is important to be aware of sensitivities. Commonly, sensitivities manifest in the form of abstract symptoms like fatigue, weight loss, constantly runny nose, and a general feeling of being unwell, which can make it challenging to track down the offending substance.
In the case of an intolerance, someone's body lacks the substances necessary to process something. A well known example of intolerance is lactose intolerance, caused by a lack of the enzyme needed to digest milk. When someone with lactose intolerance consumes dairy products, the results can be quite uncomfortable and often very unpleasant, as his or her digestive system struggles to cope with the milk.
Allergies, sensitivities, and intolerances should all be taken seriously. In some cases, there are treatments available which can help to reduce the severity of the response to something, and in some cases eliminate the response altogether. In other instances, there may be no treatment available, in which case it is important to be outspoken to avoid exposure to the offensive substance.