Short answer: Swallowing your own saliva does not break a Jain fast.

Details with tradition notes:

• Common principle (both Digambara and Shvetambara): Upavasa/Chauvihar/Atthai forbid taking “external” food or drink. Saliva is produced by one’s own body (internal dravya), so merely swallowing it is not counted as drinking and does not infringe the fast.
• Digambara: Even during nirjala upavasa (waterless fast), swallowing natural saliva is permitted. Deliberately creating or bringing moisture from outside (e.g., rinsing/gargling and then swallowing) would violate a waterless fast.
• Shvetambara: The same practical rule applies. Natural swallowing of saliva is acceptable; intentional moistening by sucking cloves/cardamom, lozenges, chewing gum, or swallowing after mouth-rinsing counts as taking a liquid and breaks a water-fast.

Important restraints:

• Do not intentionally stimulate saliva to ease thirst (chewing anything, flavored mouth-fresheners, lozenges, or rinsing and then swallowing).
• Gargling and swallowing, or sucking ice/stones, breaks a water-fast.
• Spitting unnecessarily is discouraged due to hygiene and possible himsa; if you must expel phlegm for health, do so discreetly and hygienically away from sacred spaces.

Essence: Natural, unavoidable swallowing of one’s own saliva is allowed; introducing or intentionally generating liquids to swallow is not.