Injecting under the skin

General information about the equipment, not medical advice. The directions that came with your medicine and the person who prescribed it come first, every time.

What the layer is

Under the skin and above the muscle there is a layer of fat. A subcutaneous injection puts the medicine there, where it is absorbed more slowly and more steadily than it would be from muscle.

How thick that layer is varies enormously between people and between sites on the same person. That is the whole reason needle length is a clinical decision rather than a preference.

Why the advice about angles changed

The old instruction to pinch a fold of skin and go in at forty five degrees came from an era of longer needles. With a 12mm or 13mm needle, going straight in risked reaching muscle on a lean person, so you lifted the fat away from the muscle first and came in shallow.

Short needles removed the problem. A 4mm pen needle is shorter than the distance to muscle at the usual sites on almost everyone, so it goes straight in at ninety degrees and the pinch becomes unnecessary. This is why diabetes guidance in Australia and internationally moved to the shortest available needle.

If you are using a longer needle, the older technique may still apply. Which applies to you depends on the needle you have and on your build, and it is a question for your prescriber rather than a rule you can take off a page.

Rotating sites

Injecting into the same spot repeatedly changes the tissue there. It can become lumpy or hardened, and tissue in that state absorbs unpredictably, which makes the medicine itself less consistent.

The fix is to move. Work systematically rather than randomly, so you can actually remember where you have been, and give each area time before you come back to it. Which areas are available to you is part of what your prescriber should have set out.

Feel the area before you inject. If it is lumpy, hard, bruised or sore, use somewhere else and mention it at your next appointment.