Pollen is the name for microspores of seed plants like ragweed, grasses and trees that wind or insects carry in the process of fertilization. People with a sensitivity to pollen may be exposed by breathing in the tiny spores or react to injections of the material meant to help desensitize the allergy-prone patient. The National Institute of Environmental Health Sciences states that only a few species of the thousands of varieties of seed-bearing plants produce allergic reactions. Side effects of pollen can range from minor irritation to shock and even death.

Swelling

One side effect of pollen injections for treatment or testing is site swelling. The slight swelling and redness at the injection site is common and isn’t problematic unless it persists for more than 24 hours or is more than 4 to 5 centimeters in diameter. If the swelling and redness is that large, it will be uncomfortable and should be treated with cool compresses and antihistamines. The swelling serves as a warning to decrease the dosage before the reaction becomes dangerous. Drugs.com states that the dosage should be reduced to a lower level that had not caused such a reaction for the next two to three weeks before a slight increase in dosage is again attempted.

Sneezing

The most common side effect of breathing in pollen is sneezing. Sneezing may be quickly followed up with a runny nose, itching eyes and a scratchy throat. Sneezing and the accompanying nose and throat irritations are due to histamine production, which dilates small blood vessels in the nose and makes the nasal passages swell and feel congested. Hopkins Technology states that while most people react to pollen ingestion by forming mucus around the offending particles and transporting them down the throat to be swallowed up or coughed out, about 5 percent of the population are allergy-prone and react with sneezing, nasal congestion and irritated eyes and throat.

Asthma

For those who are sensitive to plant pollen in the air and react with seasonal allergy symptoms, the condition can become chronic and turn into asthma. Sneezing and irritated eyes and throat can turn into a serious respiratory disease with coughing, wheezing and difficulty breathing. Bronchial passages constrict, too much mucus is produced and the bronchial tubes may be irritated until infected. Hopkins Technology states that immediate medical attention is needed when the above “hay fever” symptoms include difficulty breathing or a fever results.

Anaphylactic Shock

The most serious side effect of pollen injection is the systemic reaction called anaphylactic shock. Immunotherapy and allergic skin tests could cause a closing of breathing passages, requiring an immediate response with epinephrine-hydrochloride intramuscular injection to counteract the reaction, according to Drugs.com. This life-threatening reaction usually occurs within minutes of the injection with allergenic extracts and therefore the injections should only be administered in a medical office where a respirator and other emergency response equipment is available.