Even if people were wearing masks, it is nearly impossible to maintain a safe distance in a crowd.
And being in a crowd, close together puts you at a greater risk for infection.
Philadelphia's Department of Public Health urges anyone who participated in a protest to:
* Monitor for symptoms such as fever, cough, shortness of breath
* Try to stay away from people for 14 days
* If you can't stay away, wear a mask and maintain at least 6 feet distance from others
* Get tested 7 days after being in a crowd
* And you need not say you were protesting. Just tell the testing site you were around someone who may have COVID-19.
Keep in mind, with coronavirus you can be infected but not have symptoms.
However, you can still pass the virus onto other people such as family members or friends, who could wind up in the hospital.
Most experts believe we will see some kind of spike in cases due to the demonstrations.
Philadelphia is supposed to move into the yellow phase as of Friday.
Mayor Jim Kenney has not said officially yet if that will happen.
"Certainly the numbers are trending in that direction. I would have to see what happens today, tonight, tomorrow, Friday, to see where we're at from a crowd point of view," said Kenney.
He said the numbers are trending in the right direction, however, admitted concern about a big spike in cases due to the size and intensity of the protests, with so many unmasked people.
Protestors urged to get COVID-19 tests in about 7 days