What is a delayed reaction to a cortisone injection?: Understanding Post-Injection Side Effects

October 11, 2025 •

4 min read

While many patients experience immediate relief, approximately 1 in 5 people may feel increased pain or irritation in a phenomenon known as a 'cortisone flare,' the most common form of a delayed reaction to a cortisone injection. This temporary aggravation of symptoms can be startling but is typically short-lived and does not indicate failure of the treatment.

Quick Summary

Delayed reactions to a cortisone injection can include a temporary 'cortisone flare,' localized skin changes, and less frequent systemic effects like mood swings or blood sugar spikes. Understanding the timing and symptoms of these reactions can help manage expectations and identify when to contact a healthcare provider.

Key Points

Cortisone Flare: Temporary increase in pain and inflammation, typically lasting 1–3 days post-injection.
Localized Skin Changes: Hypopigmentation (skin lightening) or fat atrophy (skin dimpling) can appear weeks or months later and may last up to a year.
Systemic Effects: Absorbed cortisone can cause temporary mood changes, insomnia, or elevated blood sugar, particularly in diabetic patients.
Rare but Serious Complications: Watch for signs of infection (worsening pain, fever, swelling) or tendon damage, especially with frequent injections.
Management: For common flares, rest and ice are effective. For persistent or severe symptoms, seek immediate medical advice.

A cortisone injection is a common and effective treatment for localized inflammation in joints and soft tissues, offering relief for conditions like arthritis, tendinitis, and bursitis. While the injection often provides rapid relief due to a local anesthetic mixed with the steroid, some patients may experience delayed side effects. These delayed reactions can be concerning, but most are minor and resolve on their own. However, it is important to distinguish between normal, delayed effects and rare, serious complications like infection.

The Cortisone Flare: The Most Common Delayed Reaction

The most frequent delayed reaction following a cortisone injection is known as a 'cortisone flare' or 'steroid flare'. This reaction typically occurs within the first 24 to 72 hours after the injection and is characterized by a temporary worsening of pain and inflammation in the treated area. A cortisone flare is not a sign of treatment failure but rather an irritant response to the medication itself.

Causes of a Cortisone Flare

Crystallization: The corticosteroids in the injection are formulated as slow-release crystals, designed to provide long-term inflammation relief. In some cases, these crystals can irritate the synovial tissue in the joint or the surrounding soft tissue, causing a temporary inflammatory reaction and an increase in pain.
Gradual Action: Unlike the immediate effects of the anesthetic, the steroid's anti-inflammatory action is gradual. The initial increase in discomfort may be more noticeable once the numbing agent has worn off, before the steroid's full effect takes hold.

Management of a Cortisone Flare

Resting the injected area to reduce stress on the joint or tendon.
Applying ice packs to the site for 15–20 minutes at a time to reduce inflammation and numb the area.
Taking over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, if approved by a doctor.
Knowing that the flare is usually brief, with symptoms subsiding within 1 to 3 days as the steroid begins to work.

Localized Reactions with a Delayed Onset

Besides the cortisone flare, other delayed reactions can manifest at the injection site, becoming noticeable weeks or even months after the procedure.

Skin and Tissue Changes

Hypopigmentation: In this condition, the skin around the injection site becomes lighter or paler. This is more common in individuals with darker skin tones and can be a side effect of the steroid's effect on pigment-producing cells. While it can last up to a year, it often improves over time.
Fat Atrophy: A divot or indentation in the skin may form due to the localized loss of subcutaneous fat tissue. This sunken appearance is generally benign and may improve within a year.
Skin Thinning: Cortisone can cause the skin in the injection area to become thinner and more fragile, increasing the risk of easy bruising.

Tendon Issues

Repeated or improperly placed injections, particularly near a tendon, can lead to a weakening of the tendon structure. This increases the risk of a tendon rupture, a serious complication that necessitates immediate medical attention. For this reason, doctors usually limit cortisone injections to no more than three or four per year in a single area.

Systemic Delayed Reactions

Although localized reactions are more common, some individuals experience systemic side effects as the cortisone is absorbed into the bloodstream.

Affecting Blood Sugar and Mood

Temporary Blood Sugar Increase: Patients with diabetes must monitor their blood sugar levels closely for several days following a cortisone shot, as the steroid can cause a temporary, noticeable increase.
Mood and Sleep Disturbances: In some cases, cortisone can cause mood swings, anxiety, depression, or insomnia, which can start within a week and last up to 10 days.
Facial Flushing: A feeling of warmth and redness in the face and upper body can occur and typically lasts less than 24 hours.

Other Systemic Effects

Menstrual Changes: Some women report longer or heavier periods in the days or weeks following an injection.
Adrenal Suppression: With prolonged or high-dose oral steroid use, but also a risk with frequent injections, the adrenal glands can produce less natural cortisol. This can lead to fatigue, weakness, and other symptoms.

Rare but Serious Delayed Complications

While infrequent, certain delayed reactions require immediate medical attention.

Infection

Though rare with sterile technique, an infection at the injection site can occur and presents with symptoms that worsen over time, such as increasing pain, swelling, warmth, redness, pus, or fever.

Delayed Allergic Hypersensitivity

Cortisone can, paradoxically, cause an allergic reaction, though it is rare. A delayed (Type IV) hypersensitivity reaction is mediated by T-cells and can manifest hours or days later as a chronic eczematous eruption. A history of previous cortisone exposure increases the risk of sensitization.

Comparison of Delayed Cortisone Injection Reactions


Reaction Type	Typical Onset	Common Symptoms	Duration	Management
Cortisone Flare	24–72 hours	Increased pain, swelling, inflammation at site	1–3 days	Rest, ice, OTC NSAIDs (as advised)
Hypopigmentation	Weeks to months	Skin lightening at injection site	Up to 1 year or longer	Often resolves on its own
Fat Atrophy	Weeks to months	Skin dimpling or sunken appearance	Up to 1 year or longer	Often resolves on its own
Elevated Blood Sugar	Hours to days	High blood glucose levels	Days	Close monitoring, medication adjustment (diabetics)
Mood/Sleep Changes	Within 1 week	Anxiety, insomnia, mood swings	Up to 10 days	Self-resolving, but discuss with doctor
Infection	Days to weeks	Worsening pain, swelling, redness, fever	Ongoing without treatment	Immediate medical care, antibiotics

Conclusion

While a common and effective treatment, cortisone injections can result in various delayed reactions ranging from a mild, temporary 'flare' to rare but serious complications. The most frequently observed delayed effect is the short-lived cortisone flare, which typically resolves with rest and ice. More long-term localized effects include skin and tissue changes, though these also tend to improve over time. Awareness of these potential delayed reactions allows for proper symptom management and timely communication with a healthcare provider, especially if signs of infection or other serious complications arise. Understanding the expected timeline and nature of post-injection symptoms is key to a smooth recovery and successful treatment outcome. For authoritative information on cortisone shots, consider consulting reputable sources such as the Mayo Clinic.

Frequently Asked Questions

A cortisone flare is the most common type of delayed reaction to a cortisone injection. It involves a temporary increase in pain and inflammation that appears within 24 to 72 hours, as opposed to happening immediately.

Delayed reactions vary in onset. A cortisone flare typically starts 24 to 72 hours post-injection, while skin changes like hypopigmentation can take weeks or months to appear. Systemic side effects like mood changes often occur within a week.

To manage a cortisone flare, rest the affected area and apply an ice pack to reduce swelling and pain. Over-the-counter pain medication may also help, but it's best to consult your doctor before taking anything.

Yes, a cortisone shot can cause a temporary increase in blood sugar levels that can last for several days, particularly for individuals with diabetes. Diabetics should monitor their levels closely during this time.

Skin changes like hypopigmentation (lightening) or fat atrophy (dimpling) are often not permanent. While they can last up to a year, many patients see improvement as the cortisone disperses and the body heals.

You should contact your healthcare provider immediately if you experience signs of infection, including intense pain, worsening swelling, fever, or pus at the injection site. Also, seek medical advice if your symptoms are not improving after a few days.

Yes, although it is rare, cortisone can cause a delayed (Type IV) allergic hypersensitivity reaction, which is T-cell mediated and can appear days later as an eczematous skin rash.