Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.

Do-Eun Lee, MD, has been practicing medicine for more than 20 years, and specializes in diabetes, thyroid issues and general endocrinology. She currently has a private practice in Lafayette, CA. 

 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.

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.

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.

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:

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:

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:

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:

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.

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

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.

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American Association of Diabetes Educators. Strategies for insulin injection therapy in diabetes self-management.

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

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 males. J Diabetes Investig. 2013;4(3):287–296. doi:10.1111/jdi.12035

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

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

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

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