After receiving an injection, some people experience symptoms at the injection site on the skin. This reaction is a common adverse effect of vaccines, Botox injections, biologics, and chemotherapy.

Injections and intravenous (IV) infusions are central to many treatments and vaccines. In many cases, people receive injections without any side effects or reactions. However, some people experience allergic reactions at the site of the injection.

These are different from systemic reactions, which sometimes include fever or headaches. Injection site reactions occur just around the point on the skin in which a person received an injection.

This article explores injection site reactions in more detail, including types, causes, and treatment. It also discusses when someone should speak with a doctor.

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Different injections containing various substances, vaccines, and medications can lead to different injection site reaction symptoms.

Injection site reactions may involve:

However, these symptoms may vary depending on the type of injection, a person’s immune system, and the drug a medical professional is administering.

Vaccines

People may receive vaccine injections to reduce their risk of certain infections. Any vaccine can have side effects. However, according to the Centers for Disease Control and Prevention (CDC), most of these are mild and get better within several days.

Depending on the type of vaccine, symptoms may include:

  • arm soreness
  • swelling
  • skin redness or discoloration
  • a feeling of warmth around the injection site
  • low-grade fever

Pain is another common symptom. A 2021 review found that 84–92% of people felt pain at the injection site within seven days of receiving either the Pfizer or Moderna vaccine for COVID-19. Around 1 in 10 people experienced redness, while 11–15% reported swelling.

The same review found that some reactions to vaccines can occur one week after vaccination and cause skin inflammation for several days.

Botox

People often receive Botulinum toxin (Botox) injections for cosmetic reasons, but it can also serve a medicinal purpose, such as managing chronic migraine.

According to the United Kingdom’s National Health Service (NHS), injection site reactions for a Botox injection often include:

The adverse effects are often moderate. Symptoms may be more severe in people who need Botox to treat a health condition, as they typically require a higher dose.

Biologics

People with autoimmune disorders, such as psoriasis or multiple sclerosis, may need to take IV biologics. These are medications that reduce immune activity to help the body manage symptoms of these conditions.

According to a 2020 study on five biologics, injection site reactions from these medications may involve:

  • skin redness and discoloration
  • pain
  • itching
  • bruising

Chemotherapy

Chemotherapy is a type of cancer treatment. According to the American Cancer Society (ACS), it can have a range of side effects, which may include injection site reactions. However, doctors do not administer all chemotherapy drugs intravenously. Some people may take these medications orally.

Chemotherapy injections may cause typical injection site reaction symptoms, including:

  • skin redness and discoloration
  • swelling
  • itching
  • tenderness
  • warmth

However, chemotherapy drugs sometimes cause a symptom known as extravasation, which can lead to blistering, severe pain, and skin damage. Extravasation may develop within around 12 hours of a person receiving injected chemotherapy.

Different types of injection site reactions occur for different reasons.

Vaccines

Injection site reactions occur when a person’s immune system reacts to a vaccine injection. Often, this does not involve an allergic reaction, which is an immune response to a certain trigger that is too aggressive. According to an older article, typical inflammation causes injection site reactions.

Inflammation occurs when the immune system responds to pain, injury, or foreign substances. As injections technically involve a small skin injury and the introduction of a foreign substance, such as a vaccine, inflammation is a natural response.

Botox

An injection site reaction where the needle meets the skin is also a natural reaction to a Botox injection.

However, Botox is a toxin that temporarily paralyzes certain muscles. Eyelid droopiness or limited facial muscle movement may occur if a practitioner injects too much Botox or it moves from the intended site.

Biologics

The exact causes of injection site reactions due to biologics are unclear, according to a 2020 study.

A 2023 review of 158 studies found that injection site reactions occur in 0.08–15.5% of people who take biologics, depending on the particular drug.

Out of the 16 medications in the review, the one responsible for the most injection site reactions was canakinumab, while secukinumab had the least. However, in most of the studies that included data on how many people stopped using the medication, the reactions were not strong enough to warrant stopping the injections.

Chemotherapy

Extravasation may occur when a small amount of chemotherapy medication leaks from a blood vessel to the area just beneath the skin around the injection site.

A 2020 review cites studies that indicate extravasation occurs in 4.7–6.5% of people who receive chemotherapy treatment and is more likely in younger people.

According to the NHS, injection site reactions may get better within 3–5 days. The following measures can help manage injection site reactions:

  • Applying a cold compress to the area, such as an ice pack, may help to reduce swelling.
  • Antihistamines can help to reduce the body’s reaction to the injection.
  • People who take regular injected medications, such as biologics, may benefit from switching injection sites every time they receive or self-administer an injection.

If adverse effects after an injection do not pass in a few days or continue to get worse, a person should contact a medical professional. Those who receive regular biologics or chemotherapy injections may be able to use a different medication.

Symptoms of a severe allergic reaction, or anaphylaxis, require immediate medical attention.

Anaphylaxis: Symptoms and what to do

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

  • hives
  • swelling of the face or mouth
  • wheezing
  • fast, shallow breathing
  • a fast heart rate
  • clammy skin
  • anxiety or confusion
  • dizziness
  • vomiting
  • blue or white lips
  • fainting or loss of consciousness

If someone has these symptoms:

  1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
  2. Dial 911 or the number of the nearest emergency department.
  3. Lay the person down from a standing position. If they have vomited, turn them onto their side.
  4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one.

Injection site reactions may occur due to vaccines, Botox, biologics, and chemotherapy. Any injection can cause an injection site reaction if the immune system responds to the skin injury or the substance in the injection.

Symptoms often include skin redness and discoloration, swelling, and itching at the injection site. Cold compresses and antihistamines may help reduce these symptoms.

People should contact a doctor if symptoms do not resolve or get worse. If anaphylaxis develops, a person should call 911 immediately.