How Do You Know If You Did a Bad Injection?

October 10, 2025 •

4 min read

Medication errors at home, which include incorrect self-administration, can occur at rates between 2% and 23% [1.4.1]. Learning how do you know if you did a bad injection is crucial for identifying complications early and seeking appropriate medical care when necessary.

Quick Summary

Knowing if an injection went wrong involves watching for signs beyond mild, temporary pain. Key indicators include severe or worsening pain, spreading redness, fever, pus, nerve sensations like tingling, or symptoms of a severe allergic reaction.

Key Points

Normal vs. Serious Symptoms: Mild pain, itching, and redness are common, but severe pain, fever, pus, or spreading redness indicate a serious problem [1.5.1].
Infection is a Key Risk: Any break in the skin can lead to infection. Look for increasing warmth, swelling, pain, and pus, and contact a doctor if these occur [1.7.3].
Nerve Damage Signs: A sharp, electric shock-like pain during injection or persistent numbness/tingling afterward suggests a nerve may have been hit [1.9.3].
Anaphylaxis is an Emergency: Difficulty breathing, facial swelling, and widespread hives are signs of a severe allergic reaction that requires calling 911 immediately [1.7.1].
Rotate Injection Sites: To prevent tissue damage like lipohypertrophy (fatty lumps), it's crucial to rotate where you give injections, especially for daily medications like insulin [1.11.3].
Prevention is Critical: Using proper hygiene, new sterile needles for every shot, and correct technique are the best ways to avoid complications [1.6.2, 1.6.3].
When in Doubt, Seek Help: If symptoms worsen instead of improve after a day or two, or if you have any concerns, it is always best to contact a healthcare provider [1.2.2].

Understanding Self-Injections and Potential Risks

Many people rely on self-injected medications for managing chronic conditions like diabetes or autoimmune disorders. While a vital part of healthcare, administering injections carries risks if not performed correctly. An injection is considered "bad" when it leads to complications beyond the expected mild and temporary discomfort. These complications can range from minor skin irritation to severe issues like infection, nerve damage, or an allergic reaction [1.2.2]. Knowing the difference between a normal reaction and a sign of trouble is essential for safety.

Most injections, whether subcutaneous (into the fat layer under the skin) or intramuscular (into the muscle), cause minor side effects like temporary soreness, slight swelling, itching, or redness at the injection site [1.5.1, 1.8.4]. These symptoms typically resolve within a few hours to a couple of days [1.5.1]. However, certain signs indicate a more significant problem that may require medical attention.

Signs of a Serious Injection Complication

A bad injection can manifest in several ways. It's important to monitor the injection site and your overall well-being after administering a shot.

Localized Infection

Any puncture of the skin can introduce bacteria, leading to an infection [1.3.3]. While rare with proper sterile technique, infections are a serious risk. Signs of an infection at the injection site include:

Increasing pain, redness, swelling, or warmth [1.2.2]
Pus or clear fluid draining from the site [1.7.3]
Red streaks spreading from the injection area, which could indicate a serious infection called cellulitis [1.2.2]
Fever, muscle aches, and significant fatigue [1.2.2, 1.7.1]
A painful, pus-filled lump under the skin known as an abscess [1.2.2]

Nerve Injury

If a needle hits a nerve, it can cause immediate and sometimes lasting symptoms. Incorrectly choosing an injection site, such as the wrong quadrant of the gluteal muscle, can increase the risk of hitting major nerves like the sciatic nerve [1.3.2, 1.5.4]. Symptoms of nerve damage include:

A sharp, shooting, or electric shock-like pain during the injection [1.9.3]
Persistent numbness, tingling, or a burning sensation [1.5.4, 1.9.1]
Muscle weakness or difficulty moving the limb [1.9.2]

Hitting a Blood Vessel

Injecting into a blood vessel, particularly an artery, is dangerous and can lead to serious complications [1.2.3]. While aspiration (pulling back the plunger to check for blood) was once common, it is no longer recommended for most injections [1.3.4]. Signs that you may have hit a blood vessel include:

Visible blood in the syringe [1.2.3]
Prolonged or significant bleeding at the site that is difficult to stop.
Injecting into an artery can cause severe pain, and the blood may appear bright red and frothy [1.10.2].

Severe Allergic Reaction (Anaphylaxis)

Though rare, any medication can cause a severe, life-threatening allergic reaction known as anaphylaxis [1.5.4]. Symptoms develop suddenly and require immediate emergency medical attention (Call 911) [1.5.1].

Difficulty breathing, wheezing, or throat swelling [1.7.1]
Widespread hives or rash [1.5.1]
Swelling of the face, lips, or tongue [1.2.2]
Dizziness, fainting, or a rapid heartbeat [1.2.2]
Nausea, vomiting, or diarrhea [1.2.2]

Tissue Complications: Lipohypertrophy and Lipoatrophy

Repeatedly injecting in the same spot, a common issue with insulin injections, can damage the fatty tissue beneath the skin.

Lipohypertrophy: This is the more common complication, characterized by a firm, rubbery lump of fatty tissue that builds up at the injection site. Injecting into these areas can lead to erratic medication absorption [1.11.1, 1.11.3].
Lipoatrophy: This is a rarer complication where the fat tissue breaks down, leaving a visible dent or depression in the skin [1.11.2, 1.11.4].

Comparison of Injection Reactions


Issue Type	Common Signs	Recommended Action	Source(s)
Minor Site Reaction	Mild pain, redness, itching, small lump or bruise at the site. Usually appears within 24 hours and resolves in 1-2 days.	Apply a cold compress. Use over-the-counter pain relievers if needed. Monitor the site.	[1.2.2, 1.5.2]
Site Infection	Worsening redness, severe pain, warmth, swelling, pus drainage, red streaks, fever.	Contact a healthcare provider immediately. Antibiotics may be necessary.	[1.2.2, 1.7.3]
Nerve Contact/Injury	Sharp, shooting pain or electric shock sensation during injection; persistent tingling, numbness, or weakness.	If pain is severe and persistent, or if weakness develops, consult a healthcare provider.	[1.5.4, 1.9.2]
Allergic Reaction (Anaphylaxis)	Difficulty breathing, swelling of face/lips/tongue, widespread hives, rapid heartbeat, dizziness.	Call 911 or go to the nearest emergency room immediately. This is a life-threatening emergency.	[1.5.1, 1.7.1]
Lipohypertrophy	Firm, raised, or rubbery lumps of tissue under the skin at a frequent injection site.	Rotate injection sites. Do not inject into the affected area until it heals. Consult a healthcare provider.	[1.11.1, 1.11.3]

How to Prevent a Bad Injection

Prevention is the best strategy. Following proper procedures significantly reduces the risk of complications.

Practice Good Hygiene: Always wash your hands thoroughly before preparing an injection. Clean the injection site with an alcohol swab and let it dry completely [1.6.1, 1.6.3].
Use Sterile, Single-Use Equipment: Never reuse or share needles and syringes. Always use a new needle and syringe for every injection [1.6.2].
Rotate Injection Sites: If you perform injections frequently, systematically rotate the locations. This is crucial for preventing lipohypertrophy and tissue damage. Keep a log to track your sites [1.6.3, 1.11.3].
Use Correct Technique: Ensure you are using the correct needle length and angle for the type of injection (subcutaneous vs. intramuscular). Your healthcare provider should train you on the proper technique for your specific medication [1.6.3].
Know Your Anatomy: Be aware of the proper locations for injections to avoid major nerves and blood vessels. For example, gluteal injections should only be in the upper-outer quadrant [1.9.3].

Conclusion

While most self-injections proceed without issue, knowing how to spot the signs of a bad injection is a critical part of self-care. Mild soreness and redness are common, but severe pain, signs of infection like fever and pus, persistent numbness, or symptoms of an allergic reaction are red flags. If you experience any of these serious symptoms, it is crucial to seek prompt medical attention. By following safe injection practices—including proper hygiene, site rotation, and using sterile equipment—you can significantly minimize your risk of complications.

For more information on safe injection practices, you can visit the Centers for Disease Control and Prevention (CDC). [1.6.4]

Frequently Asked Questions

A normal, mild reaction includes temporary redness, swelling, itching, or soreness right around the injection site. These symptoms usually peak within 24-48 hours and then fade on their own [1.2.2, 1.8.3].

An infected site will have increasing redness, pain, warmth, and swelling. You might also see pus or fluid draining from the area, have red streaks spreading from the site, or develop a fever [1.7.3, 1.2.2].

Accidentally injecting into a muscle (intramuscular) instead of fat (subcutaneous) can be more painful and may cause the medication to be absorbed faster than intended. While generally not dangerous for a one-time error, it can affect the drug's efficacy and timing. Using the correct needle length and technique helps prevent this [1.11.3].

A small, temporary lump can be part of a normal inflammatory reaction [1.5.2]. However, if you inject frequently (like with insulin) and develop a persistent, rubbery lump, it could be lipohypertrophy, which requires you to stop injecting in that area and consult a doctor [1.2.2].

Signs include a sudden, sharp, shooting, or 'electric shock' pain during the injection, followed by lingering tingling, numbness, or weakness in that limb [1.5.4, 1.9.3].

Go to the ER or call 911 immediately if you experience signs of a severe allergic reaction (anaphylaxis), such as trouble breathing, swelling of the face or throat, widespread hives, severe dizziness, or a rapid heartbeat [1.5.1, 1.7.1].

Apply firm, steady pressure to the site with a clean gauze or cotton ball for several minutes. Most minor bleeding stops quickly. If the bleeding is heavy, prolonged, or spurts, you may have hit a blood vessel and should seek medical advice [1.2.3].

Yes, in rare cases. A severe infection can lead to an abscess or tissue damage. An injection that causes significant nerve injury can result in chronic pain, numbness, or weakness [1.3.2]. Repeatedly injecting in the same spot can cause permanent tissue changes like lipoatrophy [1.11.4].