It's understandable to be skeptical of claims that your sheets won't stink after you've slept in them for a week. And some of the language Miracle Brand uses in their marketing sounds overblown. For example, they say their sheets contain "natural silver fiber," but where in nature are you going to find cotton fibers mixed with silver?
Despite the odd wording, current science backs up the idea that silver-infused fibers can kill bacteria. Though Miracle Brand doesn't share the testing data behind their claim of 99% effectiveness, the theory is sound.
However, they also claim that the bacteria-fighting power of their sheets means you can go up to three weeks without washing them. This is a bad idea.
Even if the silver-infused fibers could completely eliminate bacteria from your bedding, microbes aren't the only things that make your sheets dirty. They're still filling up with dead skin, hair, and natural oils, not to mention day-to-day dirt and grime.
You're probably better off washing your Miracle sheets after 10 days at most. That still buys you a bit of extra time, since you need to launder regular bed sheets once a week, but it won't completely transform the way you do laundry. Your silver-treated bedding will have less odor between washes, though.
It's worth noting that a cotton-and-silver blend isn't your only option when it comes to antimicrobial bedding. For example, bamboo sheets also inhibit bacterial growth, making them good for your hair and skin.
