How Needle Size Affects Diabetes Control

Man injecting himself with insulin in belt area

 Trish Gant / Doring Kindersley / Getty Images

If you find using an insulin pen injector to be painful, you may be able to eliminate this problem by switching to a different needle size. Studies have found short, thin needles deliver insulin as effectively as longer, thicker ones and may be more comfortable to use. Your healthcare provider can help you make an informed decision about whether using a different needle is an option for you and which size to switch to.

Longer Is Not Better

Injectable medications such as insulin and glucagon-like peptide-1s (GLP-1s) are most effective when injected just below the skin into fatty tissue so the body can easily absorb and use it. Therefore, a long needle isn't necessary. In fact, if insulin is injected into muscle tissue it will be used up more quickly than is ideal, which potentially could lead to hypoglycemia. What's more, if a needle pierces muscle tissue it can cause pain, bruising, and bleeding.

Studies show needle length doesn't affect blood sugar control. Needles as short as 4 millimeters [mm]) do not appear to impact the function of administered insulin and may actually have advantages over longer needles, since again, they're can't reach muscle tissue, making it less likely people who used insulin will skip self-injections to avoid pain.

Some people with diabetes worry that a shorter needle may allow insulin to leak from the injection site, but research has shown this to be an unfounded concern.

The thickness of a needle—gauge—and not leaving the needle in the skin long enough are more likely to affect insulin leakage than its length.

Needle Sizes

Insulin pen needles range from 4 mm to 12 mm in length and 29 to 32 gauge in diameter. The lower the number of millimeters, the shorter the needle, while the higher the gauge, the thinner the needle. On average, human skin is 1.6 mm to 2.5 mm thick, so a 4 mm needle will easily breach the skin layer.

4 mm

The smallest, thinnest needle is the nano 4 mm, 32 gauge needle, which is about as thin as two strands of hair. The risk of injecting into muscle tissue is very rare when using this needle, which should not require pinching the skin while injecting (done to pull the fatty tissue away from the muscle for a more accurate injection).

The 4 mm is considered suitable for adults and children. Options in this length include:

  • GlucoRx 4mm: FinePoint Pen Needles Universal Fit 4 mm 31G
  • BD Micro-Fine Pen Needles 4 mm
  • NovoFine Plus 32G 4 mm

6 mm

The 6 mm mini needle usually comes in a gauge of 31 or 32, making it as thin as the 4 mm option. Options include:

  • Unifine Pentips 6 mm
  • Novofine Pen Needles 6 mm
  • MyLife Penfine Needles 6 mm
  • GlucoRx FinePoint Pen Needles Universal Fit 6 mm 31G

8 mm

The 8 mm needle is still short and very thin, with an average gauge of 31, but typically requires pinching the skin to get an most accurate dose.

Options in this length include:

  • GlucoRx FinePoint Pen Needles Universal Fit 8 mm 31G
  • BD Micro-Fine Pen Needles 8 mm
  • MyLife Penfine Needles 8 mm
  • Novofine Pen Needles 8 mm
  • Unifine Pentips 8 mm

10 mm to 12 mm

The 10 to 12 mm length was once the standard needle size, and many people are still accustomed to this length. These needles are very thin, with a gauge size ranging from 29 to 31. There's a small chance that a longer needle such as the 10 mm or 12 mm size may negatively impact thinner patients who have less subcutaneous fatty tissue to get through before reaching the muscle. Ask your healthcare provider if this length is right for you.

Options in this length include:

  • Unifine Pentips (10mm)
  • MyLife Penfine Needles (10mm)
  • FinePoint Pen Needles Universal Fit 10 mm 31G
  • FinePoint Pen Needles Universal Fit 12 mm 31G
  • BD Ultra-Fine Pen Needles 12.7 mm 29G

The Food and Drug Administration cautions against removing both the outer and inner needle covers from standard pen needles—and paying special attention to needle technique when switching needles, so as not to receive an underdose.

Reducing Injection Pain

To prevent or lessen pain discomfort while using an insulin pen, regardless of needle size, you can:

  • Let insulin come to room temperature. Cold insulin can sting—remove it from the fridge 15 minutes before injecting.
  • Allow the alcohol to dry. If you use alcohol to clean and prepare your injection site, allow it to dry before injecting your insulin.
  • Try not to tense up. Before injecting, take deep abdominal breaths and mentally work to relax the muscles at the site where you'll be injecting.
  • Don't jabs. Rather, aim for quick, direct penetration. Inject at a 90-degree angle to your skin and do not change the direction of the needle once you are in the injection site.
  • Rotate injection sites. Move the injection site by one inch with each dose to prevent soreness, irritation, or formation of a painful lump.
  • Press, don't rub. If an injection hurts painful, apply pressure to the site for a few seconds, but do not rub it: This could increase insulin absorption and put you at risk of hypoglycemia.

A Word From Verywell

Always use a new needle for each injection, as repeated use of the same needle increases the risk of infection and may cause the needle to weaken. A weak needle may bend or break during injection or become dull, leading to bruising or bleeding. It's also important to properly dispose of used needles in a specially marked sharps container for medical waste.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Association of Diabetes Educators. Strategies for insulin injection therapy in diabetes self-management.

  2. Hirsch LJ, Gibney MA, Albanese J, et al. Comparative glycemic control, safety and patient ratings for a new 4 mm x 32G insulin pen needle in adults with diabetes. Curr Med Res Opin. 2010;26(6):1531-41. doi:10.1185/03007995.2010.482499

  3. Hirose T, Ogihara T, Tozaka S, Kanderian S, Watada H. Identification and comparison of insulin pharmacokinetics injected with a new 4-mm needle vs 6- and 8-mm needles accounting for endogenous insulin and C-peptide secretion kinetics in non-diabetic adult malesJ Diabetes Investig. 2013;4(3):287–296. doi:10.1111/jdi.12035

  4. Præstmark KA, Stallknecht B, Jensen ML, Sparre T, Madsen NB, Kildegaard J. Injection technique and pen needle design affect leakage from skin after subcutaneous injectionsJ Diabetes Sci Technol. 2016;10(4):914‐922. doi:10.1177/1932296815626723

  5. Gibney MA, Arce CH, Byron KJ, Hirsch LJ. Skin and subcutaneous adipose layer thickness in adults with diabetes at sites used for insulin injections: implications for needle length recommendations. Curr Med Res Opin. 2010;26(6):1519-30. doi:10.1185/03007995.2010.481203

  6. Food and Drug Administration. Caution when using pen needles to inject medicines: FDA safety communication.

By Barbie Cervoni MS, RD, CDCES, CDN
Barbie Cervoni MS, RD, CDCES, CDN, is a New York-based registered dietitian and certified diabetes care and education specialist.