In Ayurveda, the traditional healing system of India, Ayurvedic aromatherapy complements diet and lifestyle choices to balance your body based on your dosha and sub-doshas.
Ayurveda has five concepts, called elements:
The five elements combine to form three energies (humors or doshas) that govern the body:
You have a predominant dosha, plus each dosha has five sub-doshas, giving you a unique constitution. Ayurveda treats you based not only on your symptoms but also on your constitution. Thus, two people with the same symptoms may receive different treatments.
For the use of aromatherapy and essential oils in Ayurveda, the best resource I have found is Ayurveda & Aromatherapy: The Earth Essential Guide to Ancient Wisdom and Modern Healing. This book explains how to use essential oils in a way consistent with Ayurvedic principles.
For example, essential oils either add heat or have a cooling effect on the body. Blue chamomile is cooling, lavender is neutral, and thyme is hot. So, thyme would increase pitta, which is hot. Neutral oils balance the body and can either cool you down or warm you up.
Ayurveda also classifies essential oils as either wet or dry. Wet oils (for example, geranium and rose) mix well with water, while dry oils (for example, citrus oils and pine) float more on the surface of water. Because vata is dry, dry oils increase vata and wet oils decrease it, while wet oils increase pitta and kapha. Again, some oils, such as lavender, are neutral.
The book goes on to list essential oils appropriate for specific imbalances and also gives you ways to use the oils, including Ayurvedic massage.
Aromatherapy: A Complete Guide to the Healing Art also contains a chapter about aromatherapy and Ayurveda, including lists of balancing oils for each dosha:
I recommend Young Living Essential Oils.