Injection site rotation: why it matters and a simple plan

If you inject something several times a week, the spot you choose matters. Using the same few square inches over and over can leave lumps under the skin that change how well the next dose is absorbed. The fix is simple: rotate.

What goes wrong without rotation

The best-studied problem is lipohypertrophy: a rubbery, thickened lump of fatty tissue that builds up where injections keep landing. It's been studied mostly in people who inject insulin, which is the largest group of people injecting under the skin every day.

In one study of 430 people injecting insulin, nurses examined their injection sites:

• Nearly two-thirds (64%) had lipohypertrophy.
• Among people who rotated sites correctly, only 5% had it.
• Of those who had it, 98% didn't rotate or rotated incorrectly.
• Reusing needles also raised the risk, especially past five uses.

Injecting into a lump is a problem because absorption from it is less predictable: the same dose can do more one day and less the next. In that study, people with lipohypertrophy had far more unexplained low blood sugars and swings.

The same logic applies to peptides and testosterone: you want each dose to be absorbed the same way as the last.

The usual sites

Under the skin (subcutaneous), for most peptides:

• Abdomen: at least two finger-widths away from the belly button, on either side.
• Love handles / flanks: the soft area at the sides of the waist.
• Thighs: the front and outer part of the upper thigh.
• Back of the upper arms: if you can reach comfortably.

Into the muscle (intramuscular), often used for testosterone oil:

• Glutes: the upper outer area.
• Deltoids: the shoulder muscle, for small volumes.
• Thighs: the outer middle of the thigh muscle.

A simple rotation plan

Injection-technique recommendations written by 183 diabetes experts from 54 countries put it simply: never inject into a lump, and rotate sites correctly to prevent them. A common way to do that:

1. Split each area into sections. For the abdomen, think of four quarters around the belly button.
2. Use one section for a while, then move on in the same direction each time (for example, clockwise).
3. Space injections within a section at least 1 cm (about a finger-width) from the last one.
4. Don't go back to the exact same spot until it has had a good rest.
5. Use a new needle every time.
6. Check your sites now and then: run your fingers over them and look for lumps or hard patches. Skip any lump until it goes away.

If you take two compounds the same day, give each its own spot rather than injecting both into the same place.

Signs to stop and get checked

Rotation prevents lumps, but some signs need a clinician:

• redness, warmth or swelling that spreads or gets worse over a day or two
• pus, fever, or a hot, painful lump (possible infection or abscess)
• a site that stays painful long after the injection

How the app helps

Remembering which side you used three days ago is the hard part. Protocol Unlocked suggests the least recently used site for each dose on the Today screen, gives two doses on the same day different sites, and shows a body map of which sites are resting, recently used or ready again.

For technique, read Injecting under the skin and Oil injections (testosterone).

Sources

• Blanco 2013, Diabetes Metab (lipohypertrophy prevalence and risk factors). PMID 23886784
• Frid 2016, Mayo Clin Proc (New Insulin Delivery Recommendations). PMID 27594187