Deliberately Inhaling Incense Breaks the Fast
Q: Is it permissible for the fasting person to smell perfume and ʿoūd [type of incense]?
A: Shaykh ʿAbd al-ʿAzīz ibn Bāz: One should not inhale ʿoūd. There is no problem with [smelling] the other types of perfumes, except bukhūr [incense]. As for ʿoūd itself, it should not be inhaled because some of the people of knowledge say that if ʿoūd is inhaled it breaks one’s fast. This is due to some of its elements going to the brain [therefore affecting the fast]. It also actively spreads [throughout the body]. But smelling it unintentionally does not break one’s fast.
Commentary of Ustādh Mūsá Richardson:...