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How to choose the right length needles for insulin injections: one simple trick

If you inject insulin, what length needle do you use? We recently asked the Diabetic South Africans community and here’s what they said:

How do you choose the right length needle?

If you’re like many people with diabetes, you might think that your needle length is a matter of preference – and that longer needles are less painful. But in fact, shorter pen needles and syringes have been proven to effectively deliver the insulin dosage into the subcutaneous fat tissue (where you inject) while reducing the risk of injecting into muscle. Here’s the research to support this.

The average skin thickness is no more than 2.8mm thick for nearly all patients at all injection sites. With a 4mm needle, you can inject straight in. This means a single-handed, no-pinch injection technique that is easier and more convenient. It also means you can inject in places that are hard to reach when using two hands, like the back of the arm.

Why does needle length matter?

  • Shorter needles (4 to 5mm) have been proven to reduce the risk of intramuscular injections. Injecting into the muscle rather than the fat can be dangerous as it causes the insulin to be absorbed very quickly, which can lead to low blood sugar. 
  • Shorter needles allow for a wider injection zone. You can inject into places that are awkward to inject into if you need two hands (like the upper arm).
  • They make the injecting process easier as you don’t need a skin fold or pinch up when using a short needle, you can just inject straight into the skin.
  • Shorter needles are more comfortable because they are less painful (there’s less chance of injecting into the muscle, which hurts).

Can having the right length needle help your blood glucose control?

Intramuscular injections – injecting into muscle by mistake – can lead to the insulin being absorbed rapidly, which can then lead to low blood sugar levels. Insulin is absorbed so rapidly in the intramuscular layer (the muscles) because there are so many blood vessels found there. 

What length needles do you use? Comment below or let us know on Diabetic South Africans!

More information about good injection technique

This is part of a series on injection technique offered by BD.

This article was brought to you with unconditional scientific support by BD.

Disclaimer: The medical information on this website is not advice and should not be treated as such. You must not rely on the information on this website as an alternative to medical advice from your doctor or other professional healthcare provider. If you have any questions about your medication, please consult your doctor.


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Sweet Life is a registered NPO/PBO (220-984) with a single goal: to improve diabetes in South Africa. We are funded by sponsorships and donations from aligned companies and organisations who believe in our work. We only share information that we believe benefits our community. While some of this information is linked to specific brands, it is not an official endorsement of that brand. We believe in empowering people with diabetes to make the best decisions they can, to live a healthy, happy life with diabetes.