An allergy occurs when your body recognizes a foreign substance and begins to attack it.  For instance, suppose you are allergic to dust mites.  If you are exposed to the mites, your body will release histamines as well as other chemicals to fight them.  This produces an allergic reaction, often in the form of a runny nose, itchy eyes and sneezing.

Allergen immunotherapy is a common choice of therapy for allergy sufferers.  A small amount of allergen is injected in to the body, enabling your body to form antibodies against the substance.  The shots are commonly given in the upper arm, but may be given in the hip as well.  Patients can experience a slight itching or develop a raised red mark at the injection site.  If the reaction is significant, the dose will be lowered during the next visit.

Patients will be prescribed an Epi-pen prior to the first visit.  They are asked to carry the Epi-Pen at all times once the therapy begins.  Patients should stay in the waiting room for at least 10 minutes after injections, and are often asked to stay for twenty.

Allergy shots are usually given twice a week for the first few weeks.  After those first weeks, the shots are given only once a week.  This is considered the build-up phase, and can take three or more months to complete.  A patient's symptoms may briefly increase during the first weeks of allergen immunotherapy. 

After the dose has reached a therapeutic level, the allergy shots are given every 2 to 4 weeks.  This is called the maintenance phase.  Allergy relief may be seen by six months, but for many it can take up to a year or more.  Some patients receive allergy shots over a course of three to five years.  If you have severe asthma, allergen immunotherapy is not recommended.  Allergy shots are not used for those with food allergies.