LONDON — What’s being billed as the future of skin care starts suspiciously like a visit to the dentist: with a mouthwash gargle. That’s to eliminate debris that may interfere with a good saliva sample, from which DNA will be extracted and serums tailored to one’s genetic blueprint.

The test is from a company called GeneU (pronounced “gene you”) and performed at its nine-month-old shop on New Bond Street, which looks like a cross between a science fiction movie set and a silver-gray-and-red-dipped Apple store — perhaps fittingly, because the DNA test is done by a flash-drive-size microchip. It’s administered by one of a handful of improbably dewy-skinned beauties who also happen to have Ph.D.s.

Unlike other DNA tests, which are sent to labs and take at least two weeks to complete, GeneU’s in-store test is done in 30 minutes. Currently, it looks only at variations in two genes: one that contains instructions for how fast your body degrades collagen and the other for antioxidant protection.