Smelling pleasant fragrances such as perfume, rose, musk, or lavender does not invalidate the fast of a fasting person. The acts that invalidate the fast are those substances that reach the stomach through the mouth or the nose. A scent, however, is not a substance that enters the body in a nourishing or substantive manner; therefore, smelling something is not considered an act that breaks the fast.
Imam al-Nawawī (may Allah have mercy on him) states in his work al-Majmūʿ:
“There is no harm for a fasting person in smelling roses or engaging with pleasant fragrances, because a scent is not a substance of a type that would invalidate the fast.”
(al-Majmūʿ, vol. 6, p. 341)
At times, people may unknowingly inhale substances such as dust, smoke, or insect spray. This also does not invalidate the fast, as it is not possible to completely avoid such matters.