The first question about a potential romantic partner is the question that doesn’t need to be asked: What do they smell like? Our olfactory glands often beat our eyes to the punch, but, because pressing your nose against the sweatshirt of a stranger is frowned upon and you sniffing a Tinder pic on your iPhone doesn’t accomplish much, we sometimes can’t answer that question about our dates. Enter Smell Dating, the only start-up in America with a self-explanatory name. The service allows people to sort through potential lovers by smell using a very old fashioned tool: The U.S. Postal Service.

Here’s how it works: Smell Dating sends you a shirt and requests that you wear it for three days and three nights without deodorant. Once this is accomplished, you send the shirt back and, in return, the company sends you swatches of t-shirts worn by other people looking for a mate. You whiff up the mystery matches’ bouquets and, voila the matches begin. The whole thing costs $25 and a bit of dignity.

While it may sound ridiculous, Smell Dating is working with a very powerful force: biology. For years scientists thought that humans were “optical animals” with great vision and an undeveloped sense of smell. But the scientific literature has gone through a major revision: We know now that smells play a huge role in sexual attraction and mating selection. How exactly this works, however, is still a bit of a mystery.

Some scientists argue that there are actually a small number of human genes that determine how desirable you are to a mate and humans can actually be drawn to these genes by smell. Olfactory communication, how the body reacts to smell, plays a role here — smells cause such a reaction that even if you can’t see what you’re smelling, olfactory signals still create an emotional response. Perfect, if all you’re doing is smelling bits of a t-shirt instead of making eyes at each other at a bar.

Olfactory receptors send signals to the brain’s neocortex, which processes the smell, and the limbic system, which triggers emotions. Meanwhile, the body is also reacting to pheromones — the chemical messengers that emit from a body, into the air, triggering behavioral and physiological responses in other people. There are two types of pheromones: Signal pheromones act as attractants and repellents, and primer pheromones produce longer lasting changes in behavior. Primer pheromones release hormones, which are connected to sperm and testosterone production in males and follicle maturation in females. This is the stuff that gets you hot and bothered.

However, if you’re itching to get your hands on 10 shirts from strangers, you’ll have to resort to your own means for now. Smell Dating just closed its registration for its first rounds of clients, but you can sign up and be notified to when it will be open again. If you’re a guy, it’s not a bad idea — studies have shown that women rank odor as more attractive than looks. For guys, while smell is hyper compelling — particularly if a women is ovulatingexperiments reveal that a pretty face still trumps a tremendous odor.