What are the problems with subcutaneous injections?

October 12, 2025 •

4 min read

According to research published in the Diabetes Technology Society, up to 62% of people with diabetes who use insulin injections may develop lipohypertrophy, a significant complication. This highlights just one of the critical problems with subcutaneous injections that can affect both patient comfort and therapeutic effectiveness.

Quick Summary

This article explores the various problems associated with subcutaneous injections, detailing issues such as injection site reactions, improper drug absorption, lipohypertrophy, and patient discomfort. It emphasizes the importance of correct technique and site rotation to mitigate risks and improve treatment outcomes.

Key Points

Lipohypertrophy: Repeated injections in the same area can cause fatty lumps that impair drug absorption and lead to erratic medication effects, especially with insulin.
Pain and Discomfort: Factors like medication temperature, pH, viscosity, and injection speed can contribute to pain, stinging, or aching at the injection site.
Incorrect Absorption: Injecting into scarred, bruised, or lipohypertrophied tissue can result in inconsistent or delayed absorption of the medication.
Infection Risk: Without proper hygiene, bacteria can enter the injection site, potentially causing localized infections like abscesses or cellulitis.
Proper Technique is Key: Correct injection angle, speed, and site selection, along with using a fresh needle, are crucial for minimizing pain and ensuring optimal drug delivery.
Rotation Prevents Problems: Regularly rotating injection sites is the most effective way to prevent tissue damage like lipohypertrophy and ensure consistent absorption.

Understanding Subcutaneous Injections

Subcutaneous (SC) injections involve administering medication into the fatty tissue layer just beneath the skin (the hypodermis). This route is favored for drugs like insulin, some blood thinners, and biologics because it allows for slower, more sustained absorption into the bloodstream compared to intramuscular or intravenous injections. Despite their widespread use and relative convenience, several issues can arise if the injection is not administered correctly or managed properly over time. The most common problems range from minor, localized reactions to more serious complications that can impact medication efficacy.

Injection Site Reactions

Injection site reactions are the most frequently reported issue with subcutaneous injections and can cause discomfort or be visually distressing to the patient.

Pain, Stinging, and Bruising

Pain and bruising are common issues. Pain can be caused by various factors, including the medication's properties (e.g., pH, viscosity, temperature), poor technique, or hitting a sensitive nerve or blood vessel. Some medications have chemical properties that cause a burning or stinging sensation during injection. Bruising can occur when a small blood vessel is nicked during the injection process.

To minimize pain: Ensure the medication is at room temperature before injecting, use a quick and firm insertion motion, and select injection sites with fewer nerve endings, like the outer thighs over the inner thighs.
To reduce bruising: Avoid rubbing the injection site after administering the medication. Apply gentle pressure with a cotton ball or gauze instead.

Lipohypertrophy

Lipohypertrophy is the buildup of fatty tissue and scar tissue at injection sites that are repeatedly used. It presents as a firm, rubbery, or lumpy mass under the skin. Patients often prefer injecting into these areas because the nerve endings are less sensitive, but this perpetuates the problem.

Impact on Absorption: Injecting into an area of lipohypertrophy impairs the absorption of medication, leading to unpredictable and inconsistent drug effects. For insulin users, this can cause erratic blood glucose levels, increasing the risk of both hyperglycemia and hypoglycemia.
Prevention: The primary prevention strategy is strict injection site rotation. Healthcare providers should inspect injection sites regularly to identify early signs of lipohypertrophy.

Infection

While rare, any breach of the skin can introduce bacteria and cause an infection. Signs of an injection site infection include increased pain, redness, swelling, warmth, and potentially pus draining from the site. Severe infections, like cellulitis or abscesses, require immediate medical attention.

Prevention: Always use sterile technique by washing hands thoroughly and cleaning the injection site with an alcohol swab. Use a new, sterile needle and syringe for every injection and never share needles.

Absorption and Efficacy Issues

The effectiveness of subcutaneous medication depends heavily on consistent and reliable absorption, which can be compromised by improper technique or tissue conditions.

Inconsistent Absorption Rates

Several factors can cause the body to absorb medication at an inconsistent rate, leading to unpredictable drug levels and treatment outcomes. These factors include injecting into compromised tissue (like a lipohypertrophy site), injecting too quickly, or administering large volumes.

Injecting at an Incorrect Depth

Inserting the needle at the wrong angle or depth can affect where the medication is deposited. Injecting too shallowly into the intradermal layer can lead to irritation and swelling, while accidentally injecting into the deeper, more vascularized muscle tissue can cause the medication to absorb too quickly, potentially leading to adverse effects.

Complications and Patient Discomfort

Beyond immediate physical issues, psychological and systemic problems can arise.

Needle Anxiety and Phobia

For many patients, especially those who must self-inject regularly, needle anxiety can be a significant barrier to treatment adherence. This fear can lead to poor technique or a reluctance to inject, impacting health outcomes. Strategies like distraction and using smaller needles can help.

Allergic Reactions

Some individuals may have an allergic reaction to the medication itself or to components within the injection device, such as latex. Allergic reactions can range from localized hives to a severe, life-threatening anaphylactic reaction.

Comparison Table: Proper vs. Problematic Subcutaneous Injection


Aspect	Proper Subcutaneous Injection	Problematic Subcutaneous Injection
Site Selection	Rotates between healthy areas, avoiding scars or lumps.	Repeatedly uses the same spot, ignoring bruising or lipohypertrophy.
Needle Insertion	Inserts needle quickly at a 90-degree angle (or 45 for thin patients).	Inserts slowly or at an incorrect angle, causing more pain and trauma.
Medication Absorption	Consistent and predictable, as drug is delivered into healthy fatty tissue.	Inconsistent and delayed, especially in lipohypertrophy sites.
Pain Level	Minimal pain due to proper technique and site choice.	Increased pain, stinging, or aching from poor technique or medication temperature.
Risks	Minimal risk of infection and complications.	Higher risk of infection, bruising, abscesses, and lipohypertrophy.
Patient Adherence	Improves patient confidence and encourages adherence to therapy.	Decreases patient willingness to self-inject, impacting adherence.

Best Practices to Avoid Injection Problems

Practice Strict Site Rotation: Use a rotation schedule (e.g., quadrant system) and leave at least an inch between new injection sites.
Master Proper Technique: Get training from a healthcare professional on the correct injection angle, speed, and pinching technique.
Ensure Correct Temperature: Allow refrigerated medications to warm up to room temperature for 15-30 minutes before injection to reduce stinging.
Maintain Hygiene: Always wash your hands and clean the injection site with an alcohol wipe beforehand.
Use Fresh Needles: Never reuse a needle or syringe. Needles dull after one use and increase the risk of pain and tissue damage.
Inspect and Palpate: Before each injection, visually inspect and palpate the intended site to check for lumps, bruising, or hardening.

Conclusion

While subcutaneous injections offer a safe and effective route for many medications, understanding and addressing potential problems is essential for successful therapy. Issues like lipohypertrophy, pain, bruising, and inconsistent absorption can be largely prevented through meticulous attention to proper injection technique and site rotation. Empowering patients with the right knowledge and tools to manage these issues not only improves comfort but also ensures consistent medication delivery, leading to better overall treatment outcomes and higher patient adherence.

For more detailed information on injection techniques, consult authoritative sources like the Centers for Disease Control and Prevention.

Frequently Asked Questions

Lipohypertrophy is the formation of a lumpy, fatty mass under the skin caused by repeatedly injecting medication, such as insulin, into the same spot. Injecting into these areas impairs drug absorption and can make medication less effective.

You can reduce injection pain by letting refrigerated medication warm to room temperature, ensuring a quick and confident needle insertion, rotating injection sites, and using a new, sharp needle for each injection.

Site rotation prevents the development of lipohypertrophy and other tissue damage. It ensures that medication is absorbed consistently and predictably with each dose.

Injecting into bruised, scarred, or otherwise damaged tissue can hinder proper medication absorption. You should always select a healthy, uncompromised injection site.

To prevent infection, always wash your hands thoroughly before preparing for an injection. Use a fresh, sterile alcohol pad to clean the injection site and allow it to air-dry completely before inserting the needle.

Yes. Injecting at an incorrect angle can cause the medication to be delivered too shallowly into the skin (intradermally), causing irritation and swelling, or too deeply into the muscle, which can affect the absorption rate.

If you notice a lump, stop injecting into that specific site immediately and for several months. Begin rotating to other healthy sites and inform your healthcare provider, who can assess the lump and provide guidance.

Used needles and syringes should be placed in a designated sharps container, a puncture-proof container with a tight-fitting lid. Contact your local health department or pharmacy for guidelines on proper disposal.