Can I use saline as a re-wetting drop in my eye?

Sterile saline (0.9% sodium chloride, the standard formulation) matches the salt concentration of tears. Putting it in your eye briefly is safe.

However, it makes a poor re-wetting drop:

• No viscosity — it drains through the puncta within seconds.
• No buffering agent — straight saline can feel slightly stingy on a dry eye.
• No preservative — opened multidose bottles can become contaminated after 7 days.

For emergencies (out of re-wetting drops, eye uncomfortable): 1–2 drops of saline directly into the eye are safe. For routine use, buy purpose-made re-wetting drops — they cost the same as saline and work much better.

One use where saline is the right answer: rinsing a lens if you have just dropped it and have no other solution nearby. Rinse, inspect, reinsert.