What causes erythema and edema after an injection?

From the Guidelines

Redness and swelling after an injection are typically caused by a local immune response to the injected substance, which can be managed with self-care measures and, if necessary, medical attention. The introduction of foreign substances through an injection can trigger an inflammatory response, leading to blood vessel dilation and fluid accumulation in the area, resulting in erythema and edema 1. This reaction is usually harmless and resolves on its own within a few days.

Management of Local Reactions

To manage these symptoms, apply a cold compress to the injection site for 10-15 minutes several times a day to reduce inflammation and discomfort. You can take over-the-counter pain relievers like acetaminophen (Tylenol) at a dose of 500-1000 mg every 6 hours or ibuprofen (Advil, Motrin) at 400-600 mg every 6-8 hours if needed for pain or swelling. Keep the area clean and avoid rubbing or scratching it.

When to Seek Medical Attention

If the redness and swelling are mild, these measures should be sufficient. However, seek medical attention if you develop:

• Severe pain
• The redness spreads more than 2 inches from the injection site
• Symptoms worsen after 48 hours
• You develop a fever above 100.4°F (38°C)
• Pus appears at the injection site

These guidelines are based on the most recent and highest quality evidence available, prioritizing morbidity, mortality, and quality of life as outcomes 1. It's essential to note that while most injection site reactions are harmless, they can occasionally be a sign of a more serious issue, such as an infection or allergic reaction, which would require prompt medical evaluation and treatment.

From the FDA Drug Label

DERMATOLOGIC Rash* (including maculopapular type), pruritus Vesiculobullous eruptions, urticaria, erythema multiforme, Stevens-Johnson syndrome, alopecia Toxic epidermal necrolysis, photoallergic skin reactions ALLERGIC Syndrome of abdominal pain, fever, chills, nausea and vomiting; anaphylaxis; bronchospasm [see CONTRAINDICATIONS] Serum sickness, lupus erythematosus syndrome, Henoch-Schonlein vasculitis, angioedema Hypersensitivity AlIergic reactions in the form of rash, urticaria, angioedema, and, rarely, erythema multiforme, Stevens-Johnson syndrome, or toxic epidermal necrolysis have been observed.

The causes of erythema and edema after an injection are likely due to hypersensitivity reactions or allergic reactions to the drug, as evidenced by reports of rash, urticaria, angioedema, and erythema multiforme in the drug labels 2 3.

From the Research

Causes of Erythema and Edema after an Injection

• Erythema and edema after an injection can be caused by a local adverse drug reaction, also known as an injection site reaction (ISR) 4, 5, 6.
• ISRs are characterized by symptoms such as swelling, redness, and pain at the injection site, and can be caused by various factors, including the type of vaccine or medication administered 4, 5.
• The risk of ISR can be increased by factors such as the injection site, with deltoid muscle injections being more likely to cause ISRs than thigh injections in children under the age of 3 4.
• The introduction of acellular pertussis vaccine has been shown to decrease the risk of general side effects, but may increase the risk of ISRs 4.
• Extensive limb swelling reactions after diphtheria-tetanus-acellular pertussis or reduced-antigen content diphtheria-tetanus-acellular pertussis vaccine have been shown to involve swelling of both subcutaneous and muscle tissues, with the swelling exceeding clinical measurements of skin redness and swelling 5.
• Extravasation, which occurs when a drug or fluid leaks out of a vein and into the surrounding tissue, can also cause erythema and edema, and can be managed with nursing intervention and thermal application 7.

Factors Contributing to Erythema and Edema

• The type of vaccine or medication administered can contribute to the risk of erythema and edema, with some vaccines and medications being more likely to cause ISRs than others 4, 5, 6.
• The injection site can also contribute to the risk of erythema and edema, with certain injection sites being more likely to cause ISRs than others 4.
• The age of the patient can also be a factor, with children under the age of 3 being more likely to experience ISRs after deltoid muscle injections 4.
• The use of certain medications, such as biologics, can also increase the risk of ISRs, with some medications being more likely to cause ISRs than others 6.