During the summer months, a car left in a parking lot can quickly heat up. There are some things that should never be left in a hot car, because they can be affected by high temps. Be sure to remove over-the-counter and prescription medicine. Most medicines are formulated for efficacy at room temperature; high heat can alter the chemicals and make them ineffective. The same goes for sunscreen; the heat can alter the formulation and turn your SPF into nothing more than moisturizer.