The American Academy of Dermatology says that an itch consists of a complex process that involves nerves responding to the release of histamine and sending signals to the brain. Implications of itchy skin range from insect bites to drug sensitivity.
Sensitivity to aspirin causes itchy skin. "Reactions to aspirin are often related to the drug itself, however, rather than to an allergic or immunological response to the drug," according to Dr. James T. Li of the Mayo Clinic. Symptoms appear within a few hours of taking the drug. In addition to itchy skin, a person will have hives and a runny nose. More serious signs include swelling of the lips, tongue and face, along with difficulty breathing.
Opioids, such as morphine codeine and oxycodone, provide effective pain relief. Liam Kavanagh, of the Royal Childrens' Hospital Melbourne Pharmacy Department, notes that pruritis frequently occurs after administration of opioids. Opioid receptors are located in all parts of the brain and in the spinal cord. It is thought that opioid-induced itching is a direct effect of the drug binding with the receptors. The highest incidence of itching occurs with the intravenous administration of opioids.
Physicians commonly prescribe antibiotics as treatment for bacterial infections. Some individuals have a sensitivity to these drugs. According to the Mayo Clinic, "penicillin is the most common drug allergy." Symptoms of a true allergic reaction to an antibiotic include hives, rash, itchy skin, wheezing and swelling of the lips, tongue and face. The allergic response process begins when the allergen, in this case, a medication, is ingested. A network of cells that comprise the immune system communicate and activate antibodies. As antibodies attack the allergen, they release histamine. Histamine is responsible for the symptoms, such as itchy skin.