Arthus Reaction

What Is It, Causes and More

Author:Nikol Natalia Armata

Editors:Alyssa Haag,Emily Miao, PharmD

Illustrator:Jessica Reynolds, MS

Copyeditor:Sadia Zaman, MBBS, BSc

What is an Arthus reaction?

An Arthus reaction refers to an acute, localized inflammatory response that typically occurs after vaccination. It is classified as a type III hypersensitivity reaction, which is when antigen-antibody clusters, also known as immune complexes, are formed due to an abnormal immune system response. The reaction usually presents at the site of injection after a vaccination (e.g., tetanus-diphtheria booster). In some rare instances, an Arthus reaction may result from multiple, repeated insect bites

Why does an Arthus reaction occur?

An Arthus reaction is the result of a localized inflammation of the small vessels (i.e., vasculitis) near the injection or bite site. This response occurs due to the interaction between the injected antigens and the circulating antibodies (e.g., IgG), which are created after repeated exposure to a specific antigen. As a result, immune complexes are formed around and within the blood vessels of the skin. Subsequently, activation of the complement cascade, which is part of the innate immune system, enhances the local inflammation. 

Excited Mo character in scrubs
Join millions of students and clinicians who learn by Osmosis!
Start Your Free Trial

How common is an Arthus reaction?

An Arthus reaction is not very common. However, it is possible that many cases of Arthus reactions are not reported, or even diagnosed, due to the generally mild clinical presentations.

What are the signs and symptoms of Arthus reactions?

The signs and symptoms of Arthus reactions are typically mild and usually develop within 24 hours after the exposure to the triggering factor. Most individuals present with redness, swelling, and pain. It can also subsequently lead to induration (i.e., hardening of the area due to increased fibrous tissue) localized to the affected area. In more severe cases, the redness and swelling can spread throughout the extremities, and localized hemorrhages can be observed near the site of injection. Rarely, necrosis and ulcerations of the skin have been reported in very severe cases. The signs and symptoms may persist from a week to a few months, however, they typically leave no scars after healing. 

How is an Arthus reaction treated?

The treatment is based on the severity of the reaction. Most mild cases resolve on their own and do not require medical intervention. In more severe cases, steroids and antihistamines (i.e., medication used to alleviate allergy symptoms) can be used to restrict the inflammatory response. 

What is the difference between an Arthus reaction and serum sickness?

The primary difference between an Arthus reaction and serum sickness is that serum sickness refers to a systemic reaction, whereas an Arthus reaction is only localized. Additionally, serum sickness usually presents after 6 to 15 days of being exposed to the antigen, however, an Arthus reaction is expected to appear within 24 hours of the exposure. An Arthus reaction occurs more quickly than serum sickness because the individual has already been repeatedly exposed to the antigen and has pre-existing antibodies in the circulation, whereas with serum sickness new antibodies are yet to be formed. Both an Arthus reaction and serum sickness are classified as type III hypersensitivity reactions.

Quiz yourself on Arthus Reaction

36 Questions available

Quiz now!

Watch related videos:

Mo with coat and stethoscope

Want to Join Osmosis?

Join millions of students and clinicians who learn by Osmosis!

Start Your Free Trial

Related links

Hypersensitivity skin reactions: Clinical practice
Type III hypersensitivity
Complement system

Resources for research and reference

Peng, B., Wei, M., Zhu, F. C., & Li, J. X. (2019). The vaccines-associated Arthus reaction. Human vaccines & Immunotherapeutics, 15(11), 2769–2777. DOI: 10.1080/21645515.2019.1602435 

Rixe, N., & Tavarez, M. M. (2021, September 2) Serum Sickness. In: StatPearls [Internet]. Retrieved December 2, 2021, from: 

Usman, N., & Annamaraju, P. (2021, August 22). Type III Hypersensitivity Reaction. In: StatPearls [Internet]. Retrieved December 2, 2021, from: 

Wang, M. H., Hu, A., Lee, Y. S., & Lai, C. C. (2019). Arthus Reaction. The Journal of Emergency Medicine, 56(4), 450–451. DOI: 10.1016/j.jemermed.2018.12.047