Smell is the only sense that goes directly to the limbic system, bypassing the cerebral cortex, (our intellectual part of the brain). The other senses of sight and hearing must register with the cortex before entering other parts of the brain.

Many bodily functions such as digestive activity, respiration, hormone balance, heart rate, blood pressure, stress levels, pain reduction, and memory can be regulated through the connection between the limbic system and other parts of the brain and body.

Odor messages are one of the fastest ways to achieve beneficial psychological or physiological effects. The effect of essential oils on the mind and emotions is extraordinary

The molecules of essential oils are so small that they can easily penetrate the skin and pass the blood-brain barrier. The odor molecules travel up your nose where they are trapped by olfactory membranes. These impulses are carried to the limbic system and the olfactory sensory center at the base of the brain.

From the limbic system, odor messages go to the hypothalamus, which sends messages to the other parts of the brain (pituitary, pineal, and amygdala) and body, stimulating the autonomic nervous system (ANS), endocrine system, organ functions, secretions of antibodies, neurotransmitters, hormones and enzymes throughout the body. The direct effect that smell  perhaps suggests why aromatherapy is considered one of the most valuable tools in the treatment of stress and anxiety related conditions, which can be seen as an overload of the sympathetic nervous system.