Pretty soon the cup will leak. The lemon oil will digest the plastic. All the oils that are high in Phenols are excellent for dissolving petrochemicals from the body. They must be diluted with carrier oil unless you put them on the bottom of your feet. Never dilute with water.
Water drives the oil in deeper.
If you are heating up, use any carrier oil. If you don't have carrier oil, vegetable oil from the kitchen will do. Other oils have Phenols but in smaller levels. Many of the oils are immune stimulating. The key with allergies is to keep using the oils over time.