A cortisone injection, often called a steroid shot, is a highly focused medical treatment designed to relieve localized pain and inflammation in the body. The medication used is a corticosteroid, a potent anti-inflammatory drug that mimics cortisol, a hormone naturally produced by the adrenal glands. Physicians use these injections to treat conditions like arthritis, tendinitis, and bursitis by delivering the drug directly to the irritated joint, tendon, or soft tissue. While the shot may temporarily include a local anesthetic for immediate relief, the steroid itself can sometimes cause a temporary increase in pain and swelling, known as a “steroid flare,” in the first 24 to 48 hours.
The Localized Action of Cortisone
The success of a corticosteroid injection depends entirely on the medication remaining concentrated at the site of inflammation. The drug is formulated to have a delayed-release effect, allowing it to stay in the targeted area for an extended period. Once injected, the steroid begins its work by suppressing the immune system’s localized response that causes swelling and pain. It achieves this anti-inflammatory goal by limiting the dilation and permeability of tiny blood vessels in the tissue. This action restricts the accumulation of immune cells responsible for the inflammatory cascade. By inhibiting the release of destructive enzymes and chemical mediators, the corticosteroid effectively calms the irritated tissue. The goal is to maximize this potent, localized anti-inflammatory effect before the drug naturally disperses into the rest of the body.
Why Heat Undermines the Injection
Applying heat to the injection site directly conflicts with the localized action required for the treatment to be successful. Heat is a vasodilator, meaning it causes the local blood vessels to widen significantly, dramatically increasing blood flow to the treated area. This rush of circulation acts like an accelerated clearance system for the corticosteroid. As blood flow increases, the rate at which the steroid is absorbed into the systemic circulation also increases. The drug is essentially washed away from the target joint or soft tissue much faster than intended, reducing its necessary concentration in the inflamed area. This premature systemic absorption diminishes the localized therapeutic effect, potentially leading to a less effective outcome and shorter duration of pain relief. Increased blood flow can also exacerbate the initial post-injection swelling, contributing to immediate discomfort.
Recommended Post-Injection Care
Instead of heat, the universally recommended treatment for post-injection discomfort is cold therapy, particularly during the first 24 to 48 hours. Applying an ice pack for 15 to 20 minutes at a time can help numb the area and provide pain relief. Cold works through vasoconstriction, which is the opposite of heat, helping to slow down local blood flow and support the medication’s retention at the injection site.
Activity modification is also important for optimizing the injection’s effectiveness. Patients should rest the treated area and avoid any strenuous activity or heavy lifting for at least 24 to 48 hours after the procedure. This period of rest allows the corticosteroid time to settle and begin its anti-inflammatory action without being prematurely stressed or dispersed by excessive movement.
Patients should closely monitor the injection site for any signs of complications beyond the expected steroid flare. Increasing pain, spreading redness, swelling that worsens after 48 hours, or any sign of drainage warrants an immediate call to the physician. A fever higher than 100.4 degrees Fahrenheit is another indicator that requires prompt medical attention, as these symptoms can suggest a rare, but serious, infection.