بسم الله الرحمن الرحيم
Fast breaks by eating or drinking or having intercourse in the state of fast knowingly. In case it is done unknowingly then fast does not break. Fast also breaks by administering drops in the ears. Fast also breaks by inhaler or taking vapour inside. Masturbation also breaks the fast. If a woman experiences menses during fast then it also shall break the fast. It is makrooh to use toothpowder, gul and toothpaste. However, there is no harm in applying scent, oil or kohl.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.