Can Post-Injection Pain Last a Week? Understanding When to Seek Help

October 1, 2025 •

4 min read

According to the National Centre for Immunisation Research and Surveillance, large local injection site reactions can take up to a week to completely resolve, particularly after certain booster vaccines. But beyond these specific cases, many people wonder, “can post-injection pain last a week?” The duration of pain depends on a variety of factors, from the type of injection to individual immune responses and potential complications.

Quick Summary

Post-injection pain can last for several days and may extend up to a week or more in certain scenarios, like large local immune reactions or pain flares from steroid injections. Factors like injection type, technique, and individual response influence duration. Severe or worsening symptoms, fever, or spreading redness warrant immediate medical attention to rule out complications like infection or serious reactions.

Key Points

Normal Duration: For most injections, mild pain and swelling typically subside within 1-3 days, peaking around 24-48 hours after the shot.
Prolonged Pain Causes: Pain can last a week due to factors like a strong immune-mediated reaction, a pain flare from a steroid shot, or irritation from a booster vaccine.
Treating at Home: Home remedies include applying a cold compress initially, switching to warmth after 24-48 hours, using over-the-counter pain relievers, and performing gentle movement of the affected limb.
Red Flag Symptoms: Seek medical attention for severe or worsening pain, increasing redness or swelling, fever, pus, or limited mobility that does not improve after a few days.
Injection Technique: Proper technique, such as relaxing the muscle, and factors like the medication's temperature can minimize discomfort.
Rare Complications: Very rarely, severe pain lasting over a week may indicate an infection (like an abscess) or a serious allergic reaction, requiring immediate care.

The Normal Timeline of Post-Injection Discomfort

For most routine injections, such as vaccinations or intramuscular shots, mild soreness is a common and expected side effect. This pain is primarily caused by two factors: the physical trauma from the needle entering the muscle and the subsequent immune-inflammatory response to the injected substance. This initial pain often begins shortly after the injection, peaks within 24 to 48 hours, and then gradually subsides. For the vast majority of people, this soreness disappears completely within a few days. The immune system mobilizes white blood cells to the injection site, which can cause localized inflammation, redness, and swelling. This is a sign that your body is processing the vaccine or medication as intended.

Factors Influencing Normal Pain Duration

Type of injection: Some injections, like the tetanus booster or certain COVID-19 vaccines, are known to cause more significant and longer-lasting soreness than others.
Injection site: The muscle's response can vary depending on where the injection is administered. For instance, intramuscular injections in the deltoid can sometimes be more painful than subcutaneous injections in the thigh or abdomen due to the depth and muscle mass involved.
Muscle relaxation: Tensing the muscle during the injection can increase pain and post-injection soreness.
Activity level: Keeping the injected limb moving can help improve blood flow and disperse the injected fluid, which can minimize stiffness and discomfort.

When Post-Injection Pain Lasts a Week (or Longer)

In some situations, post-injection pain can indeed persist for a week or even longer. This is not always a sign of a serious problem, but it warrants closer attention to your symptoms. Here are some scenarios where prolonged pain may occur:

Large local reactions: Sometimes referred to as an Arthus reaction, these are large, widespread areas of redness, swelling, and pain around the injection site, particularly after booster doses of certain vaccines like diphtheria or tetanus. While alarming, these reactions are typically self-limiting and can resolve within a week.
Post-injection pain flare: After a steroid injection, a localized pain flare can occur within the first 24 hours. While most resolve in a few days, some can persist for a week or two, though they usually respond to rest and over-the-counter pain relief.
Improper injection technique: If an injection is given too high or too deep, or if the needle damages a nerve or blood vessel, it can lead to more persistent pain. A blown vein, for example, can cause bruising and pain that takes longer to resolve.
Product formulation: The specific components of the injected medication, such as its pH level, volume, or other excipients, can affect the level and duration of pain. Some biologics, for instance, are associated with injection-site pain that can be managed with proper technique.
Infection: Though rare, a bacterial infection at the injection site can cause escalating pain. An abscess, a collection of pus, will result in severe pain, swelling, and fever and requires immediate medical attention.

Home Remedies for Managing Pain

For mild and typical post-injection soreness, several home care measures can help alleviate discomfort:

Apply a cold compress: An ice pack or cold pack wrapped in a cloth can be applied to the injection site for 10-20 minutes at a time, several times a day, to help reduce swelling and numb the area.
Use over-the-counter pain medication: Taking a pain reliever such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can help manage pain and inflammation. Note that ibuprofen can also have anti-inflammatory effects. Always follow the package directions and consult a doctor if you have concerns.
Keep moving: Gentle exercise of the injected limb can increase blood flow to the area and reduce stiffness. For an arm injection, try simple circular motions or arm raises.
Alternate compresses: After the first 24 to 48 hours, some people find that switching to a warm compress helps relax tight muscles and improves blood circulation.
Gentle massage: Gently massaging the area (if not too tender) can help disperse medication and loosen the muscle.

Comparison of Normal vs. Concerning Post-Injection Symptoms


Symptom	Normal Reaction	Concerning Reaction (Seek Medical Help)
Duration of Pain	Typically 1-3 days; can last up to a week for some large local reactions.	Persists or worsens significantly beyond 48 hours or lasts longer than one week without improving.
Intensity of Pain	Mild to moderate soreness or tenderness, especially when touched.	Severe, escalating pain that interferes with daily activities or is unbearable to the touch.
Redness & Swelling	Localized redness and swelling at the injection site that fades over a few days.	Spreading redness, especially with red streaks, or significantly increasing swelling.
Warmth	Mild warmth at the injection site that dissipates.	Injection site that is hot to the touch and spreading.
Fever	A mild, temporary fever can occur, especially with vaccines.	A fever of 100.4°F (38°C) or higher, especially with worsening local symptoms.
Discharge	None.	Pus or other fluid coming from the injection site.
Mobility	Mild stiffness or limited range of motion due to soreness.	Significant difficulty moving the affected limb or joint.
Other Symptoms	Generally, no other systemic symptoms.	Nausea, dizziness, headache, muscle aches, or signs of a severe allergic reaction (hives, breathing difficulty, facial swelling).

Conclusion: Differentiating Normal Discomfort from a Problem

It is common and typically harmless for post-injection pain to last for several days. In specific situations, such as large local immune reactions to booster vaccines or pain flares following steroid shots, the discomfort can linger for up to a week. Understanding the normal inflammatory response can help manage expectations. However, it is critical to pay attention to your body and recognize the signs that warrant professional medical attention. If you experience severe or worsening pain, increasing swelling or redness, fever, or any signs of an allergic reaction, it is important to contact a healthcare provider immediately. While most injections only cause a few days of minor soreness, being aware of the red flags is key to ensuring your long-term health and safety.

An excellent resource for vaccine safety and side effects is the Centers for Disease Control and Prevention (CDC).

Frequently Asked Questions

Yes, in some cases, it can be normal for post-injection pain to last up to a week. This is often associated with a strong immune response, such as with certain booster vaccines, leading to a large but harmless local reaction. Other factors like steroid injections can also cause pain that persists for a week or more.

You should see a doctor if your pain is severe, gets worse instead of better after 48 hours, or is accompanied by other concerning symptoms. Red flags include fever, spreading redness, pus, significant swelling, or difficulty moving the injected limb.

The most common causes include a normal inflammatory response from the immune system, particularly in response to some vaccines or boosters. Other factors include a pain flare following a steroid injection, incorrect injection technique, or irritation from the injected substance itself.

Yes, although it is a rare occurrence, an infection can develop at the injection site, and symptoms like fever, increased pain, and pus may appear within a week or two. Any signs of infection require prompt medical attention.

For the first 24 to 48 hours, a cold compress is generally recommended to reduce pain, swelling, and inflammation. After that period, some individuals find that a warm compress helps relax the muscle and can be soothing.

An Arthus reaction is a more intense, but usually not life-threatening, immune response that can happen after a booster vaccine, causing severe swelling and hardening of the skin. It may last several days but typically resolves within a week.

Yes, keeping the injected arm moving with gentle exercises can help reduce soreness. Movement encourages blood flow, which helps disperse the injected fluid and prevents stiffness in the muscle.