A penicillin allergy may be genetic or it may be caused by environmental factors, or both. Research shows that some people are more genetically predisposed to developing a penicillin allergy. Penicillin allergies have been found to have a significant association to a history of penicillin allergy in a first-degree relative. This means that if one of your parents has an allergy to penicillin, you have a higher chance of developing the same allergy. This risk factor is further increased if both your parents have allergies to penicillin. Scientists have also found that people with a variation in a particular protein-producing gene, known to stimulate the immune system, are at higher risk of developing an allergy to penicillin.
However, penicillin allergies do not only run in families. Scientists are still debating whether genetics or environments have a bigger influence on the development of allergies. People who are also at greater risk of developing an allergy to penicillin include those between the ages of 20 and 49 years, those who have taken penicillin frequently, people who are sick or have an infection, people with cystic fibrosis, and those who have a history of allergic reactions to other drugs.
Scientists believe that genetic factors need to coexist with other environmental factors to trigger an allergy to penicillin. Similarly, certain infections (such as infectious mononucleosis) or illnesses (such as HIV/AIDS, Epstein-Barr virus, and asthma) increase the likelihood of drug hypersensitivity.
While differences in age and sex are relatively insignificant determinants of allergies to penicillin, children are less likely to display allergic reactions to penicillin due to lower repeated exposures to this drug, in combination with an immature immune system. Likewise, elderly people are also less likely to display allergies to penicillin as a result of the involution of their immune responses.
Drug factors that increase the likelihood of sensitivity to penicillin include the degree of exposure to the drug -- with higher doses and lengthy administrations more likely to increase the risk of allergies; the route of administration -- with oral administration being safer than topical doses; and cross-sensitization -- with the establishment of sensitivities to one drug causing reactions to other drugs. Whether inherited or developed, anyone with an allergy to penicillin must avoid using this drug or risk suffering mild to severe, to life-threatening, reactions.