Reusable cloth face masks are thus far our best tool to prevent the spread of COVID-19 . Theyre also a better solution for mass use than disposable surgical masks, which are a potential source of microplastic pollution, according to a recent study published in the Marine Pollution Bulletin .

But as eco-friendly as cloth masks may be, they do become less effective at blocking the coronavirus when theyve been worn thin by repeated washing and wearing.

With this in mind, its important to look out for the signs that your mask is no longer safely filtering out the respiratory droplets that carry the virus. Besides all the homemade facial coverings weve been using, many commercially made masks come with no warning of when its time to toss the product.

So we tapped an infectious disease expert, a dermatologist, a licensed physician and a laundry expert to weigh in on all the signs you need to replace a mask. From loose straps to exposed threads, below are the warning signs your mask may be on its last legs.

The straps are worn out.

Rather than the mask fabric itself, its the elastic ear loops (or ties) that are the first place to show signs of wear especially if the mask has been exposed to high heat in the dryer, advised Hannah Yokoji, brand director of The Laundress , which sells nontoxic laundry and home cleaning products.

The biggest thing to watch out for is the straps that keep the mask in place, Yokoji said. If these ties become loose or stretched, you need to stop using it straight away, because if the mask isnt fitted properly to your face, you could be putting yourself and others in danger of COVID-19.