Break Out In Something

to suddenly start to have something, such as a rash, spots, or a sweat

After eating the spicy food, I broke out in a sweat.

She broke out in a rash after using the new soap.

to start doing something suddenly and unexpectedly, often in a violent or noisy way

The rioters broke out in violence when the police arrived.

The children broke out in cheers when the concert started.