Does the insertion of a flexible endoscope tube – lubricated with a slippery substance – into the nose and pharynx, and the use of an anesthetic spray in the throat to facilitate that, invalidate the fast of a fasting person?

Fasting is invalidated by whatever enters the nose, just as it is invalidated by whatever enters the mouth. Therefore, using a nasal endoscope during fasting may break the fast, especially if it is accompanied by liquids (such as a lubricating substance, a lens cleaner, or an anesthetic) or bleeding that the fasting person swallows, because the arrival of any of these to the stomach invalidates the fast.

However, if nothing reaches the stomach, it does not break the fast. Nevertheless, it is more cautious not to use it during the daytime in Ramadan except in cases of necessity or urgent need.