Where should insulin be administered subcutaneously?

Where to Inject Insulin

Inject insulin subcutaneously into the abdomen (preferred), thighs, buttocks, or upper arms, using a 4-mm pen needle inserted at 90° for all adults and children, rotating sites systematically to prevent lipohypertrophy. 1, 2

Recommended Injection Sites

The four approved anatomical regions for subcutaneous insulin injection are:

Abdomen (Preferred Site)

• The abdomen provides the fastest and most consistent insulin absorption and should be your primary injection site. 2, 3
• Inject at least 2 adult fingerbreadths (approximately 1 cm) away from the umbilicus 1, 2
• Stay approximately 1 cm above the pubic bone, 1 cm below the lowest rib, and extend laterally to the flanks 1, 2
• Never inject in the periumbilical zone—thin tissue here increases risk of painful intramuscular injection. 3

Thighs

• Use the upper third anterior lateral aspect of both thighs 1, 2
• The thigh has the thinnest subcutaneous layer and carries the highest risk of accidental intramuscular injection (25% risk with 8-mm needles vs. 1.6% with 4-mm needles) 4
• Lean individuals and children must use a lifted skin-fold when injecting in the thigh, even with 4-mm needles. 1

Buttocks

• Inject into the posterior lateral aspect of both upper buttocks and flanks 1, 2
• This site has the thickest subcutaneous layer, making it the safest for avoiding intramuscular injection 1, 4

Upper Arms

• Use the middle third posterior aspect of the upper arm 1, 2
• This is the least preferred site for self-injection because maintaining proper 90° angle and performing an independent skin-lift is difficult—assistance may be required. 3

Critical Needle Selection

Use 4-mm pen needles inserted at 90° for all adults and children, regardless of age, sex, ethnicity, or BMI. 1, 2

• Needles ≥8 mm carry unacceptably high risk of intramuscular injection, especially in the thigh and arm 1, 4
• If you must use needles longer than 4 mm, a correctly lifted skin-fold is mandatory to avoid intramuscular injection. 1
• Intramuscular injection causes unpredictably faster insulin absorption, leading to unexpected hypoglycemia and poor glycemic control 1, 4, 5

Site Rotation Strategy (Critical for Preventing Complications)

Divide each injection region into quadrants or halves and rotate systematically within one area before moving to another, using one quadrant per week. 2, 6

• Place each new injection at least 1 cm (one finger-width) from the previous site, rotating in a consistent direction 2, 6
• Failure to rotate properly causes lipohypertrophy (lumpy tissue) that produces slower, unpredictable insulin absorption and increased glucose variability. 2, 6
• Keep a written log of injection sites and dates to ensure proper rotation 2

Injection Technique Essentials

Pre-Injection

• Allow refrigerated insulin to reach room temperature (30–60 minutes) to reduce pain and prevent lipodystrophy 2, 6
• Wash hands and visually inspect the injection site for abnormalities 2
• If using alcohol, allow the site to dry completely before injecting 2, 6

During Injection

• Prime the pen before each dose by dialing 2 units and pressing until a drop appears at the needle tip. 2
• Insert the 4-mm needle fully at 90° in one smooth motion 2
• Press the thumb button straight down along the pen's axis, injecting slowly 2
• After the button is fully depressed, count slowly to 10 while maintaining pressure on both the button and needle to ensure complete dose delivery. 2
• Withdraw the needle straight out and dispose immediately in a sharps container 2

Skin-Fold Technique (When Needed)

• Very thin adults, young children (≤6 years), pregnant individuals, and lean persons injecting in the thigh should gently lift a skin-fold without blanching 1, 2
• The fold should be lifted with thumb and index finger without squeezing tightly enough to cause pain 2

Critical Pitfalls to Avoid

Never inject into areas with lipohypertrophy, inflammation, edema, infection, scars, or ulceration—absorption becomes slower and unpredictable. 2, 3

• Never reuse needles—they lose sterility and become damaged, causing tissue injury. 2
• Never leave needles attached to pens between injections—this causes air contamination and medication leakage. 2
• Never share insulin pens between patients—this transmits blood-borne infections. 2
• Do not inject repeatedly into the same spot 2
• Avoid bony prominences by 1–2 adult fingerbreadths 1

Monitoring and Follow-Up

Healthcare providers must inspect all injection sites at every regular visit, or at minimum annually. 1, 2, 6

• Patients should be trained to self-inspect sites and distinguish healthy tissue from lipohypertrophy 2, 6
• Bring your injection device to each clinic visit and demonstrate your technique for provider assessment 2
• Mark borders of any lipohypertrophy with skin-safe markers and avoid those areas until instructed otherwise 1
• Large bruises, persistent lumps, or ongoing pain warrant immediate evaluation 2