Nano brows, also known as microblading or eyebrow embroidery, is a semi-permanent tattooing technique that creates hair-like strokes to fill in sparse or thinning brows. The process involves the use of tiny, fine-point needles (a nanoneedle) that make up a small disposable blade and handle (a nanoblade) to scratch and deposit pigment simultaneously under your skin.

As a scientist who specializes in skincare and beauty, I can tell you that the safety of nano brows largely depends on the practitioner's skill and the hygiene standards of the salon or clinic. It's crucial to ensure that the practitioner is well-trained, certified, and follows strict hygiene protocols to prevent any risk of infection or scarring.

As for the pigments used, they are usually iron oxide-based, which are safe and commonly used in cosmetic procedures. However, some people might be allergic to these pigments, so a patch test is recommended before the procedure.

There are few studies specifically on the safety of nano brows. However, the procedure is similar to other forms of cosmetic tattooing, which have been studied more extensively. These studies suggest that, when performed correctly, such procedures are generally safe but not entirely without risks.

Potential risks include allergic reactions, skin infections, granulomas (small areas of inflammation), keloid formation (overgrowth of scar tissue), and MRI complications (the pigments may interfere with the quality of the image).

In conclusion, nano brows can be considered safe when performed by a skilled and certified practitioner in a hygienic setting, and when proper aftercare instructions are followed. However, as with any cosmetic procedure, it's essential to be aware of potential risks and to discuss them with your practitioner before proceeding.