flare up

Short definition from Wiktionary

Verb

1. 1
   To burn brightly again.
2. 2
   To become more intense suddenly.
3. 3
   To burst out suddenly, as in anger.

Noun

1. 1
   Alternative form of flare-up.
2. 2
   A sudden outbreak, outburst or eruption (originally of flame, but now used more generally of any violent activity or emotion).
3. 3
   A sudden intensification in activity.
4. 4
   An inflammation such as of tendons (tendonitis) or joints (osteoarthritis).