Nouns ending in -ou, -out, or -oux are usually masculine, but la toux is feminine.
Toux is one of the rare exceptions: learn it as it is.
Is toux masculine or feminine?
latouxexception
The rule behind it
91.5% of -ou / -out / -oux nouns are masculine
In context
Ta toux est la conséquence de ton tabagisme.
Your cough is the consequence of smoking.
Il est souvent pris de quintes de toux.
He often gets coughing fits.
Sa toux empire, il devrait arrêter de fumer !
His cough is getting worse, he should stop smoking!