Starting next week, masks will once again be required in all indoor public places on Philadelphia, city officials announced Monday. Businesses can opt out of requiring masks if they require proof of vaccination instead.

The mandate comes as the city moves up a response level, from “All Clear” to the second category: “Mask Precautions.”

Here’s what to know about the new requirement:

Where you have to wear a mask

Masks will be required in all indoor public spaces, unless the business has chosen to require proof of vaccination instead of masks.

This includes schools, childcare settings, businesses, restaurants, and government buildings, according to the Philadelphia Department of Public Health.

» READ MORE: Here’s where you still need a mask in Philly

Residents are asked to report any business not complying with the mandate.

Why is the mask mandate coming back?

With cases rising across the region, Philly has surpassed two of the benchmarks it established to move from its lowest response level and reinstate the mask mandate.

As of April 8, the seven-day average of new daily cases was 142 (the benchmark is 100), and there’s been a 60% increase in case counts over the past 10 days (the benchmark is 50%).

Health Commissioner Cheryl Bettigole said we don’t yet know whether the BA.2 subvariant will have the same impact on hospitals as the original omicron variant this past winter. But the masks, she said, are a precautionary measure.

“I suspect that this wave will be smaller than the one we saw in January. But if we wait to find out and to put our masks back on, we’ll have lost our chance to stop the wave,” she said during Monday’s news conference, announcing the new mandate.

“If we mask up now and find out that hospitalizations don’t increase in the U.S. in response to this variant the way they have in the U.K., then great. We can then take off our masks with a sense of relief. But if we fail to act now, knowing that every previous wave of infections has been followed by a wave of hospitalizations, and then a wave of deaths, it will be too late for many of our residents. This is our chance to get ahead of the pandemic.”

» READ MORE: COVID has killed more than 5,000 Philadelphians. These neighborhoods lost the most.

When does the mask mandate start?

The mask mandate begins on Monday, April 18 to give businesses a “one-week education period.”

When will the mask mandate end?

We don’t know.

The city’s COVID-19 response system has four levels: “All Clear,” “Mask Precautions,” “Caution,” and “Extreme Caution.”

According to the city’s website, the city can go back to “All Clear” — which would drop the indoor mask mandate — when two of the following items are true:

  • There are fewer than 100 average new coronavirus cases a day.

  • Fewer than 50 people are hospitalized with COVID-19.

  • Cases have increased by less than 50% in the previous 10 days.

Should I start wearing a mask indoors now?

It’s a good idea. The current case numbers in the city mean that mask-wearing is called for under city guidelines. The delayed start is to give businesses time to adjust.

So even though the new mandate doesn’t begin until Monday, you may want to start wearing a mask again indoors today.

This article has been updated since it first published. Inquirer reporter Jason Laughlin contributed to this story.