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Possible problems of insulin injection sites

Use injection sites extensively to keep the subcutaneous fat tissue in good condition.

Penetrating the skin always causes some kind of tissue reaction. Repeatedly using the same needle and same injection site aggravates the tissue reaction. Insulin in and of itself may also increase the fat tissue. It is typical that too small area is used for insulin injections. When injecting, you should leave at least a couple of finger-breadths between the previous site and the new one.

The injection sites and insulin pump cannula sites are regularly checked at the appointment. Any hardening or swelling which is not visible is located by feeling the injection sites. You should also keep an eye on the condition of the injection sites yourself and make sure that there are no emerging calluses or swelling. The most important thing is to use a wide range of injection sites and change the needle every time you inject and cannula regularly.

If you repeatedly inject in the same place, your body may react by swelling or a hardening or thickening of the fat tissue. Consequently, the absorption of insulin from the injection site becomes impaired or uneven. Equally, there wille be “inexplicable” variations in blood sugar. The swelling and thickening is called lipohypertrophy. In Finnish they are sometimes refferred to as "lipo".

Tissue loss in the injection site manifests itself as a pit in the skin, which is almost entirely void of subcutaneous fat tissue. The underlying reason is an immunological mechanism. The subcutaneous tissue reacts either to the insulin product or its additives.

Different insulin products may cause a local hypersensitive reaction resulting in the injection site becoming red, swollen, hot and possibly sore. Avoid injecting insulin in such an injection site. Less insulin will be absorbed from the area. In addition to changing the injection site, you may also need to try another insulin product.

Bruising in the injection site is caused by the needle penetrating a surface vein. Some areas have more surface veins, and you should avoid them. People who use anticoagulants are more susceptible to bruising. A drop of blood forming in the injection site is usually an indication of a surface vein broken by the needle. It is not dangerous.

A bruise or drop of blood in the injection site is not a sign of insulin entering a vein. The injection site and equipment may also have an effect on the sensitivity to bruising. You should not inject insulin into a bruised area until it has healed.

Insulin is injected into the subcutaneous fat tissue. When using 4–6 mm needles in accordance with current recommendations and correct injection technique, there is usually no risk of injecting into muscle. Previously, it was common to use 8–12 mm needles, and the risk did exist. Long-acting insulin is absorbed much faster from muscle tissue than the subcutaneous fat tissue.

Updated 17.10.2023