Christmas is a time for family. Family meals, family fights, and now―it seems― a time for finding out your family may not be your family after all. 

Last Christmas, sales of at-home DNA tests soared. It seemed people could not give their DNA to companies fast enough, while paying for the honour. Many bought it for fun, or to scratch a small itch of curiosity about their heritage. 

This year looks set to be no different. Alongside a considerable Christmas-time discount, Ancestry currently boasts that their product is ‘a gift as unique as their DNA’. Meanwhile, the BBC has described at-home tests as “The Christmas present that could tear your family apart”.

How did DNA tests fast become a go-to festive gift and, more importantly, whoever thought it was a good idea? By very design, the painless swabs have the potential to uncover a wealth of very painful family secrets ― proof of adoption, infidelity, romantic affairs. Perhaps it all ties into the festive theme of the season — Joseph wasn’t Jesus’ real father after all. Although, he never needed a DNA test to tell him that.

I’ve been signed up to the UK’s main DNA testing websites ― Ancestry and 23andMe ― for almost two years now. I am part of the UK’s first generation of IVF babies, and my sperm donor was anonymous, so I signed up to try and discover close relatives, and quickly discovered a half-sister. 

To make it clear― I am not anti-DNA testing (although I know many people are for privacy reasons, to god-knows-how-my-DNA-will-be-used reasons). Matching with my sister was one of the most amazing experiences of my life. I actively wanted to find her, and it took me half my life because I had no resources to help (bar selling my DNA to a major corporation and hoping they don’t use it to clone/frame me in the near-distant future). But while it brought me answers and joy, it was so emotionally draining that I’m terrified of ever going through it again. Therefore, it’s not something that dominates my Christmas list.

Which is why these days, I look towards this festive bump in the sales of such tests with a somewhat wary optimism. Crucially, I have no idea how many times my donor donated, so I don’t know how many siblings I have. Rather than socks or a shiny new gadget, my Christmases now offer vulnerability and promise in equal measures ― will I find another sibling? Will I find 5? Might I even find my donor? 

Of course, the surge in home DNA tests is not just a phenomenon confined to Christmas. But between Yule time, New Year’s sales, and Black Friday, it’s a busy period, as companies get paid to collect and test people’s genetic data.

If you’re reading this just before Christmas, with your eyes darting to the bottom of the tree where a test tube lies in a box, garnished with a neat bow. Don’t panic. You’re probably fine. There probably isn’t some deep-rooted family secret in your family, just lurking in the genetic shadow, and waiting to ruin this Christmas, and every one thereafter.

But let’s be clear: genetic data can be explosive, and these products have the potential to change families. Yes, it’s fun to discover that you’re 0.0000001% Icelandic, or that your risk of developing gout is 1/500. But when DNA tests are seen as a harmless hobby and cost less than a night out on 12 pubs of Christmas, genetic family secrets are becoming virtually impossible to keep. 

Whether they were insatiable, unfaithful, or infertile ― people with a genetic secret to hide need to be aware of the new world we live in. As it stands, many parents will never inform their sons or daughters of secret siblings, or an anonymous donor who is their biological parent. 

In the initial days of fertility treatment, this lack of transparency was perhaps more excusable. There was no hint that cheap and easy DNA testing would become widespread. And there was little consideration for the feelings of children resulting from anonymous donation. The medical community was still too busy self-congratulatorily wanking itself off over the marvel of artificial insemination (while encouraging potential sperm donors to do the same).  

Likewise for adoption, and infidelity. Secrets were safe, so long as children somewhat resembled their parents. But now, identity-revealing news comes in shiny wrapped boxes. And what could be more betraying than unwrapping a box from a faceless company that has the potential to break your reality apart? 

This holiday season, one page of data can re-write everything you think about your life, and the people in it. Christmas is about family, after all. They just may not be who you think. 

Louise McLoughlin is a journalist.