The essential oils are not compulsory for the cosmetics but they can bring additional benefits to the products.
However, the following shall be taken into consideration:
The essential oils should never be used undiluted and be applied directly on the skin as they are highly concentrated. They should make up 2% or less of your formulation.
The essential oil safety and contraindications information should always be checked before using essential oils. For example, they should be avoided during pregnancy, lactation, for babies as well as for people suffering from epilepsy, heart and kidney problems.