This effect will occur if Natural Cure is the Pokémon's Ability in battle when it switches out and is not suppressed; a Pokémon that obtained the Ability with Trace will have its status condition cured when it switches out, whereas a Pokémon which has Natural Cure but has been affected by Gastro Acid will not.
Generation IV onward
Natural Cure also heals any status conditions upon completing a battle (if it was in battle at the end of the battle).
Outside of battle
From Generation IV onward, Natural Cure automatically heals status conditions upon the end of a battle.
Blissey's removes all debuffs from the user every 6 seconds. This will trigger even if Blissey currently has no debuffs.
Trevenant's causes the user to recover HP every .5s for 4s, after falling below 35% HP and it also reduces the cooldowns of the user's moves by 1s every second. When the HP recovery effect ends, this ability goes on a 100s cooldown, but each time the user hits an opponent with any of its moves, this ability's cooldown gets decreased by 1s (but not more often than every .5s).
In The Power of Us, during two simultaneous disasters in Fula City, Toren and his fellow Scientists attempted to create an elixir out of Natural Cure in the Pokémon Research Pavilion. However, a blackout occurred before the solution could be finished, forcing Toren to improvise with Team Rocket's Lum Berries.
In the manga
The Pokémon is healed from its status conditions upon switching out.
Due to the user interface displaying how many of the opponent's Pokémon have status conditions, even though Natural Cure does not have an activation message, it is possible to deduce that a Pokémon had Natural Cure the next time the Poké Balls representing the opponent's party are displayed.