What is the suitable needle size for local injections in adults and children?

Suitable Needle Size for Local Injections in Adults and Children

For intramuscular injections, use 22-25 gauge needles with length varying by age: 7/8-1 inch for infants, 7/8-1¼ inches for children, and 1-1½ inches for adults; for subcutaneous injections, use 4-mm needles at 90° for all ages regardless of body habitus.

Intramuscular Injections

Adults (>18 years)

• Use 1-1½ inch, 22-25 gauge needles for deltoid injections 1
• The deltoid muscle is the preferred site for routine intramuscular injections 1
• The anterolateral thigh is an acceptable alternative site 1
• The needle must be long enough to reach muscle mass and prevent seepage into subcutaneous tissue, but not so long as to involve nerves, blood vessels, or bone 1

Children and Adolescents (12 months-18 years)

• Use 22-25 gauge needles, 7/8-1¼ inches in length 1
• The deltoid muscle can be used if muscle mass is adequate 1
• For toddlers, the anterolateral thigh is preferred with a 1-inch needle 1
• Research supports that for adolescents weighing <60 kg, a 16-mm (5/8 inch) needle is appropriate, while those weighing 60-70 kg should receive a 25-mm (1 inch) needle 2

Infants (<12 months)

• Use 7/8-1 inch, 22-25 gauge needles 1
• The anterolateral thigh is the recommended site, as it provides the largest muscle mass 1
• Insert at 90° angle using the WHO technique (skin stretched flat, needle inserted to the hub) 3

Gauge Considerations

• Narrower gauge needles (higher numbers) may reduce procedural pain 1
• Research demonstrates that 30-gauge needles are as effective as 25-gauge needles for dental blocks in children, with potentially less crying during mandibular blocks 4, 5
• For vaccines, 25 mm needles (either 23 G or 25 G) produce fewer local reactions than shorter 16 mm needles while maintaining comparable immune response 3

Subcutaneous Injections

All Ages (Adults and Children)

• Use 4-mm pen needles inserted at 90° for all patients regardless of age, sex, ethnicity, or BMI 1
• This recommendation applies to insulin and other subcutaneous medications 1
• If using needles >4 mm or syringes, employ a correctly lifted skinfold to avoid intramuscular injection 1

Special Populations Requiring Skinfold Technique

• Lean patients with BMI <19 kg/m² should use a lifted skinfold with 4-mm needles to prevent intramuscular injection 1
• Children and young adults are at higher risk for accidental intramuscular injection and should use a 2-finger lifted skinfold, particularly when the skin-to-muscle distance is less than needle length plus 3 mm 1
• Older adults may have thinner, more fragile skin but skinfold assessment should be individualized 1

Preferred Injection Sites

• Abdomen: 2 adult fingerbreadths away from umbilicus 1
• Thighs: Upper third anterior lateral aspect 1
• Buttocks: Posterior lateral aspect of upper buttocks and flanks 1
• Upper arm: Middle third posterior aspect 1

Intradermal Injections

• Use 3/8-3/4 inch, 25-27 gauge needles 1
• Administer on the volar surface of the forearm 1
• Insert with bevel facing upward at an angle parallel to the long axis of the forearm 1
• The entire bevel should penetrate the skin to raise a small bleb 1

Critical Pitfalls to Avoid

Site Selection Errors

• Never use the buttock routinely for intramuscular injections due to sciatic nerve injury risk and decreased vaccine immunogenicity from inadvertent subcutaneous or deep fat injection 1, 6
• Avoid areas with lipohypertrophy, scars, or tissue abnormalities 1, 6
• Maintain proper site rotation for patients requiring frequent injections 6

Needle Length Errors

• Too short needles result in subcutaneous rather than intramuscular deposition, reducing vaccine efficacy 1, 7
• Too long needles risk involving nerves, blood vessels, or bone 1
• In obese patients, consider that subcutaneous tissue thickness increases with BMI, potentially requiring longer needles for intramuscular injections 7

Technique Errors

• Always insert intramuscular needles at 90° angle 1, 7
• If aspiration yields blood, withdraw and select a new site 1, 6
• Avoid injecting cold medications; room temperature is preferred 1
• Never reuse needles to prevent infection 1

Device-Specific Considerations

• Pen needles with contoured bases distribute pressure more widely than posted bases, reducing injection force and pain 1
• 32-gauge needles are recommended for most adults with diabetes for reduced pain 1
• 5-bevel needle tips are preferred over 3-bevel tips to minimize skin penetration force 1