The next few months are going to be difficult for doctors, nurses, and other healthcare workers around the country who have been summoned to care for the people infected with the coronavirus. Around the world, there is a shortage of personal protective gear that will keep these workers safe as they care for patients in COVID-19 wards. While companies are scrambling to create masks and gowns, several shoe brands are donating shoes to medical professionals so they can stay comfortable as they spend long days on their feet. But demand for these shoes has been so high that many of these brands are having to place caps on the number of shoes they give away.

This week, Crocs announced that it will give away a free pair of clogs—either a Crocs at Work or Classic Crocs style—along with free shipping to medical professionals who can request a pair on the brand’s website. The company says it is prepared to donate 10,000 shoes a day through requests on its website, and also send 100,000 pairs to healthcare institutions around the country that have described a need for footwear. On Wednesday, Crocs hit its daily free pair limit. It is asking medical workers to come back at noon every day to get in line for their free pair.

Last week, Allbirds announced on Instagram that it would be donating free Wool Runners—its best known style—to healthcare workers. Anybody interested simply had to send an email to the company with their credentials and mailing address. In four days, the company donated $500,000 worth of shoes, which is about 5,000 pairs, exhausting the supply of shoes the brand had devoted to this cause.

There is a long wait-list of healthcare workers who have requested shoes, so starting March 24, Allbirds has pivoted to a “buy-one-give-one” model. Customers can bundle a shoe purchase with a donation that will split the cost of delivering a pair of shoes to someone on the list.

Clove, a brand new startup that makes shoes specifically for healthcare workers, has also started donating shoes to those on the front lines. The brand has been surprising teams of healthcare workers with free shoes in their size. Last Thursday, for instance, Clove showed up at the Thomas Jefferson University Hospital in Philadelphia at 8 a.m., right before doctors, nurses, and nurse practitioners were about to start testing patients. The company is going to donate 200 shoes and more than 1,000 compression socks during this crisis.