Simplify the following text for a Grade 3 native English-speaking person.
Original: Pain that lasts a long time is called chronic , and pain that resolves quickly is called acute . Traditionally , the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset ; the two most commonly used markers being 3 months and 6 months since the onset of pain , though some theorists and researchers have placed the transition from acute to chronic pain at 12 months .
Simplified: Pain can be acute or chronic .