I notice a lot of tattoos on people these days, though not on me. Many are on Millennials, though not on my sons. Many of the tattoos are very attractive, or moving, and I am happy to admire them on other people, especially Millennials, for all of whom I try to play the role of Supportive Mom.

I am still learning about the microbiome, and continuing to be amazed by how much has changed since I studied biomedical engineering, roughly during the horse-and-buggy days, which lasted longer in Texas. Recently I encountered macrophages, which were a type of white blood cell associated with the immune system in my old texts. They now are thought to permanently reside in all tissues, not just in blood, and to be responsible for removing old cells and toxins as well as invading microbes. They take various forms in different tissues, so for years scientists did not realize those were all related.

That assessment could change tomorrow. Science is always challenging itself, and frequently revising what it recently thought. That confuses non-scientists sometimes. Real scientific revision arise from using the scientific method, which differentiates them from alternate facts.

In any case, skin macrophages turn out to be primary storage for tattoo dye. A tattoo is a wound, or I suppose a lot of wounds, and skin macrophages rush to the site to repair the damage, lapping up as much invasive dye as they can hold and containing it, essentially forever.

Most skin cells slough off, as you may have noticed. Tattoos don’t, because they are injected into the dermis, the second skin layer, and because they are stored by the immune system. So an artful tattoo is also a self-inflicted infection, viewed through the epidermis.

Some say that tattoos strengthen your immune system, the more the merrier. That’s based on some very specific results from a single lab, though. I think we need additional research before we declare tattooing to be the Cure for the Common Cold.