What Happens If You Give a Subcutaneous Injection Wrong? Risks & Correction

October 8, 2025 •

4 min read

Subcutaneous injections are a common method for administering medications like insulin or heparin into the fatty tissue beneath the skin. However, improper technique is a leading cause of injection site reactions and other complications. Knowing what happens if you give a subcutaneous injection wrong is crucial for patient safety and effective medication delivery.

Quick Summary

An incorrect subcutaneous injection can lead to issues ranging from mild pain and bruising to more serious infections or poor medication absorption. Understanding proper technique, including needle angle, site selection, and hygiene, is key to preventing complications.

Key Points

Inconsistent Medication Absorption: Injecting into the wrong tissue depth (too shallowly or deeply) can alter the medication's absorption rate, impacting its effectiveness.
Injection Site Reactions (ISRs): Common signs of a faulty injection include temporary pain, redness, swelling, and itching at the site, often caused by shallow injection or minor tissue irritation.
Increased Pain and Bruising: Improper technique, such as hitting a blood vessel or using dull needles, can lead to increased pain and bruising, which usually resolves on its own.
Risk of Infection: Failing to maintain sterile technique, including proper hand and site cleaning, significantly increases the risk of local infection, which can lead to more serious conditions like an abscess or sepsis.
Tissue Damage (Lipohypertrophy): Repeatedly using the same injection site can cause damage to the fatty tissue, resulting in hardened lumps that can hinder future absorption.
Allergic Reactions and Systemic Issues: Though rare, an incorrect injection can trigger a severe allergic response or, in the case of some medications, a systemic issue like hypoglycemia if injected too quickly.

The Anatomy of a Subcutaneous Injection

To understand what happens when a subcutaneous (SubQ) injection goes wrong, it's helpful to first know the correct procedure. A SubQ injection delivers medication into the layer of fatty tissue located just beneath the skin (epidermis and dermis) but above the muscle. This route is used for medications that need slow, sustained absorption, such as insulin and some vaccines. The proper technique involves preparing the site, pinching a fold of skin, inserting a short, small needle at the correct angle, and slowly injecting the medication.

Common Errors and Their Consequences

Injecting Too Shallowly

One of the most frequent mistakes is inserting the needle at too shallow an angle, causing the medication to be delivered into the dermal layer of the skin instead of the fatty tissue. This can result in a localized, irritating reaction, including a red, sore, or itchy bump that can last for several days. The medication may also be absorbed less effectively, potentially impacting its intended effect.

Injecting into the Muscle (Intramuscular)

While less common with the shorter needles used for SubQ, injecting too deeply into the muscle can also have consequences. Some medications are specifically designed for slow absorption in fatty tissue. Injecting into muscle tissue, which has a richer blood supply, can accelerate absorption and increase the risk of side effects. For example, injecting insulin into the muscle can cause a rapid drop in blood sugar (hypoglycemia).

Hitting a Blood Vessel or Nerve

During an injection, it is possible to nick a small blood vessel. This typically results in minor bleeding and bruising at the injection site. While generally not serious, excessive bleeding or bruising can be a sign of poor technique or underlying health issues. In rare cases, a needle can hit a nerve, causing a sharp, radiating pain. Sticking to recommended injection sites with fewer nerve endings, like the outer thighs, can help reduce this risk.

Using Incorrect Injection Sites

Consistency in medication absorption is maintained by rotating injection sites and avoiding certain areas. Injecting into the same spot repeatedly can lead to skin irritation, discomfort, and even tissue damage known as lipohypertrophy, which creates hardened lumps. Poor site rotation can also lead to inconsistent medication absorption. Areas with existing bruising, swelling, or scars should also be avoided, as they can hinder absorption and increase pain.

Comparison of Incorrect Injection Outcomes


Incorrect Technique	Most Common Consequence	Absorption Impact	Pain Level	Associated Risks
Injecting Too Shallowly (into the dermis)	Redness, soreness, itchy bumps at site	Inconsistent or poorer absorption	Mild to moderate burning or pressure	Injection site reaction (ISRs)
Injecting Too Deeply (into the muscle)	Faster than intended absorption	Significantly faster absorption	Moderate to severe pain	Increased risk of medication-specific side effects, e.g., hypoglycemia with insulin
Hitting a Blood Vessel	Minor bleeding and bruising	Usually no impact	Brief, sharp pain	Hematoma formation
Hygienic Failure	Localized infection (cellulitis or abscess)	Poor absorption due to inflammation	Pain and warmth at site	Sepsis, scarring, tissue damage
Repeated Site Usage	Lipohypertrophy (hardened, lumpy tissue)	Inconsistent or incomplete absorption	Increased discomfort	Tissue damage, poor therapeutic outcome

How to Minimize Risks and Correct Errors

Preventing a faulty injection begins with meticulous attention to detail. Always wash hands thoroughly and clean the injection site with an alcohol swab, letting it air-dry completely. Use a fresh, sterile needle and syringe for every injection. Pinching the skin fold to separate the fatty tissue from the muscle is also a key step, especially for those with less adipose tissue.

If an error occurs, the course of action depends on the specific mistake. For a partial dose, the Centers for Disease Control and Prevention (CDC) suggests that the remainder of the dose can often be administered on the same day in a different spot. However, specific medication guidelines may differ, so consulting a healthcare provider or pharmacist is always best. For minor bruising or injection site reactions, cold compresses can help reduce swelling and discomfort.

To prevent complications, you should:

Rotate injection sites: This prevents tissue damage and scarring, which can interfere with absorption. Keep a record or use a simple system to track your injection spots.
Use the correct angle: A 90-degree angle is standard, but a 45-degree angle may be necessary for individuals with less fatty tissue.
Ensure proper hygiene: Maintain a sterile field to prevent infection. Don't touch the needle or injection site after cleaning.
Wait after injection: Hold the needle in place for a few seconds before withdrawing to prevent medication leakage.
Seek professional guidance: Always consult a healthcare professional for questions on technique or if you experience unusual symptoms after an injection.

When to Seek Medical Attention

While most minor complications like bruising resolve on their own, more serious issues require medical intervention. Symptoms of infection, such as worsening pain, increasing redness or warmth, pus, or fever, should be reported to a doctor immediately. Signs of a serious allergic reaction, like trouble breathing or facial swelling, warrant emergency medical care. Prompt attention to these warning signs can prevent serious health complications.

Conclusion

Making a mistake during a subcutaneous injection, while potentially unsettling, often results in minor issues that resolve quickly. However, understanding the specific risks—from poor medication absorption to infection—is vital for safe and effective treatment. By prioritizing proper technique, including site rotation, correct angle, and hygiene, patients can significantly reduce the likelihood of complications. Staying vigilant for signs of more serious reactions and knowing when to contact a healthcare provider ensures that any issues are addressed promptly and effectively, safeguarding the patient's well-being. Good technique is not just about avoiding pain; it's about ensuring the medication does its job correctly and safely.

Medical News Today offers an in-depth look at subcutaneous injection side effects and complications.

Frequently Asked Questions

If you suspect the injection was too shallow, a common result is a mild, localized reaction like a red or itchy bump. For a partial dose, the remainder may be re-administered in a separate spot on the same day. However, it's crucial to consult a healthcare provider for specific advice regarding your medication and to learn how to adjust your technique for future injections.

Signs of a potential infection include worsening pain, increased redness or warmth around the injection site, pus or drainage, or a fever. If you experience any of these symptoms, you should contact a healthcare provider immediately for evaluation and treatment.

While serious injury is rare, a poorly administered subcutaneous injection can cause harm. Common issues like injection site reactions or bruises are generally minor, but mistakes involving hygiene can lead to severe infections, and incorrect depth with certain medications (like insulin) can cause significant systemic effects.

To prevent bruising, ensure you use a fresh, sharp needle and insert it quickly and smoothly. Apply gentle pressure with gauze after removing the needle, but do not massage the site, especially with anticoagulant medications like heparin, as this can worsen bruising.

Lipohypertrophy is the development of hardened, lumpy tissue at the injection site, most commonly associated with repeated insulin injections. It is prevented by consistently rotating your injection sites. Always inject at least one inch away from the previous site.

A small amount of bleeding is generally not a cause for concern. It usually means you've nicked a small, surface-level blood vessel. Applying gentle pressure with a clean gauze pad will help it stop.

For most individuals, a 90-degree angle is appropriate, especially when pinching a skin fold. However, if you have very little subcutaneous (fatty) tissue, a 45-degree angle may be used to prevent injecting into the underlying muscle.