When an asthma attack occurs, you must use the inhaler.
Tips
memory
哮 (xiào) means 'to roar / wheeze', 喘 (chuǎn) means 'to gasp for breath' — 哮喘 captures asthma onomatopoeically: wheezing + gasping. Adding 病 ('illness') makes it explicit. Often shortened to just 哮喘 in medical contexts.