A tattooed QR code has three enemies: ink spread over the years, skin that stretches and ages, and a link that stops working. Design against the first two, decide carefully about the third.
Fewest dots wins. A short link produces a 21- or 25-module code; a long one needs 33 or more, with modules too small to tattoo cleanly. The Connected dot shape merges neighbours so the artist draws fewer, larger shapes with no isolated pin-points. Error correction H gives the code 30 percent slack for blur. Keep at least 3 modules of clear skin around it, and plan for a size of 4 cm or more so each module is at least 1.5 mm.
About the link: a static code to your own domain, or to a page you control, is the only one you should ever put on your body. A link to a social profile dies when the platform changes URLs. Many people point a tattoo at a short link they own so they can change the destination later; that is what lifetime editable codes are for, and it is a decision to make once, properly, before the appointment. Export SVG for the stencil.
Questions
Will a QR code tattoo still scan in ten years?
If the modules are large enough and the error correction high, the code survives the ink spreading. The bigger risk is the link: make sure it points somewhere you control.
What is the smallest a QR code tattoo can be?
Around 4 cm for a 25-module code, giving modules of about 1.5 mm. Smaller than that and lines blur together within a couple of years.
Can it be a shape other than a square?
The code itself must stay square. Decorative dots around it (round, heart) are fine as long as they stay outside the quiet zone, but every extra dot is extra ink; most tattoo artists prefer the bare code.