The injection site map
Injecting into the same patch of skin week after week is how lumps form, and lumps change how a drug is absorbed. The fix is boring: rotate, and keep a record.
The injection site map is a body map that records where each shot went. It suggests the next site based on healing time, so the same spot is not used twice in a week. Pain, swelling or bruising can be logged against each site, which turns a vague sense that one area reacts badly into a record you can show someone.
How it works, step by step
- Log the dose with its site. Every entry in the dose log carries an injection site. The map fills in as you go.
- See the suggestion. Before the next shot, the map suggests a site that has had time to heal, so you are not reusing the same spot inside a week.
- Note any reaction. If a site is sore, swollen or bruised, log it against that site.
- Look back. Over weeks the map shows which areas you lean on, and whether reactions cluster in one place.
Why rotation matters: lipohypertrophy
Lipohypertrophy is a thickened, rubbery lump of fatty tissue under the skin that forms where injections are repeated in the same place. It is studied most in insulin users, where it is common, and the findings are consistent.
| Study | Year | Journal | Design | n | Key result |
|---|---|---|---|---|---|
| Blanco et al. | 2013 | Diabetes & Metabolism | Questionnaire plus nurse examination of injection sites | 430 | 64.4% had lipohypertrophy. Of those who rotated correctly, 5% had it; of those with it, 98% did not rotate or rotated incorrectly |
| Famulla et al. | 2016 | Diabetes Care | Randomised crossover, insulin into lipohypertrophic vs normal tissue | 13 | Less insulin absorbed, and variability rose sharply (coefficient of variation 52% vs 11% for absorption). Post-meal glucose at least 26% higher |
| Frid et al. (FITTER) | 2016 | Mayo Clinic Proceedings | Expert recommendations from 183 diabetes specialists in 54 countries | n/a | Lipohypertrophy distorts absorption; do not inject into it, and correct rotation helps prevent it |
The most important number for anyone tracking results is the variability. In the Famulla study, the same dose injected into lipohypertrophic tissue was absorbed less, and far less predictably, than the same dose into normal tissue. If you are trying to judge whether a dose is working, an injection site that absorbs differently from week to week adds noise you cannot see.
A fair caveat: almost all of this evidence comes from insulin, which itself promotes local fat growth, and people with diabetes often inject several times a day. How often lipohypertrophy forms with a once-weekly GLP-1 receptor agonist or with other peptides is not well studied. The labels are clear on what to do anyway. The prescribing information for both Zepbound and Wegovy says to rotate injection sites with each dose.
Where people usually inject
For subcutaneous injections, the common sites are the abdomen (keeping about 2 inches away from the navel), the upper outer thigh and the back of the upper arm. Each area can be split into zones, and within a zone each shot goes a finger's width or more from the last. The subcutaneous glossary page and the lipohypertrophy glossary page have more. A clinician should show you technique the first time.
Why log reactions per site
Mild redness, itching or a small bruise at an injection site is common with many injectables. The point of logging them per site is pattern. "My stomach always reacts" is a feeling. Six entries over two months showing swelling on the left abdomen and nothing on the thighs is something a clinician can work with. A site that becomes hot, spreading, very painful or hard should be checked promptly, not just logged.
Who it is for
- Anyone injecting weekly or more often who wants to stop using the same favourite spot.
- People on more than one injectable, where the total number of shots per week adds up quickly.
- Anyone who has noticed a lump, a sore patch or uneven results and wants a record to show a prescriber.
How it connects to the rest of the app
The map fills in from the dose log, and the protocol planner tells it how many shots to expect each week. Each dose also names its vial in the vial tracker. Doses logged from the Apple Watch land on the same map. If you ask Remi about a reaction, it answers from your own log, including the site entries.
On your next dose, log the site and anything you notice about the last one. After a month the map will show you your habits more clearly than you would describe them. The app is on the download page.
Questions people ask
Why should I rotate injection sites?
Repeated injections in the same spot can cause lipohypertrophy, a lump of fatty tissue that absorbs drugs less and less predictably. In a 2013 study of 430 insulin users, 64.4% had it, and only 5% of those who rotated correctly did.
How does the app choose the next site?
It suggests the next site from healing time, so the same spot is not used twice in a week, based on the sites you logged with each dose.
Does lipohypertrophy happen with GLP-1 injections?
The research is almost all on insulin, and how often it occurs with once-weekly GLP-1 receptor agonists is not well studied. The Wegovy and Zepbound labels still say to rotate sites with each dose.
Where can I inject subcutaneously?
Common sites are the abdomen, avoiding about 2 inches around the navel, the upper outer thigh and the back of the upper arm. Your prescriber or pharmacist should show you technique.
Can I log a reaction at an injection site?
Yes. Pain, swelling or bruising can be logged per site, so patterns show up over time.
Sources
- Every feature, in depth, Peptide AI
- Platform capabilities, Peptide AI
- Peptide FAQ, Peptide AI
- Prevalence and risk factors of lipohypertrophy in insulin-injecting patients with diabetes, Diabetes & Metabolism, 2013
- Insulin injection into lipohypertrophic tissue: blunted and more variable insulin absorption and action and impaired postprandial glucose control, Diabetes Care, 2016
- New insulin delivery recommendations, Mayo Clinic Proceedings, 2016
- Zepbound prescribing information, Eli Lilly
- Wegovy prescribing information, Novo Nordisk
