While lemon juice is acidic, it's not strong enough to chemically break down the polymers that make up most plastics.

However, lemon juice can damage plastic cups in other ways:

* Discoloration: The acid can react with some plastics, causing them to become discolored or cloudy.

* Weakening: Prolonged exposure to lemon juice can weaken the plastic, making it more prone to cracking or breaking.

* Odor: Lemon juice can leave a lingering odor in the plastic.

It's best to avoid using plastic cups for acidic beverages like lemonade, especially if you intend to leave the beverage in the cup for an extended period.