Many people view toxins in their environment as always being around them, but never being able to enter their body. They may acknowledge that when they breathe, eat or touch toxins that some toxins may enter their body. Often the belief is held that although the toxins may enter the bloodstream, they won't be able to enter the brain, due to the blood-brain barrier.
 

The blood-brain barrier (BBB) is a membrane composed of endothelial cells packed very tightly in the brain capillaries. This restricts the passage of some substances into the brain, and protects the brain from harmful substances that may be in the blood stream. The BBB is structured to allow the nutrients required by the brain to pass through, but keeps toxic substances out of the brain. However, stress, some drugs, infections, and toxins can weaken or break down the BBB, so that toxins become able to cross it and enter the brain and the nervous system.

Additionally, there is another avenue through which toxic chemicals can have direct access to the brain and nervous system that most people are unaware exists. This other avenue is the nose-brain connection. There is no blood-brain barrier between the nose and the brain. This layer of protection is not available when we inhale the toxic chemicals that are part of our everyday experience.

The olfactory and trigeminal nerves provide a connection between the brain and the outside environment. These nerves, which are involved in sensing odours and chemicals, descend down into the nose. Inhaled toxic chemicals can enter the brain by traveling along their neural pathways.

Due to this neural connection between the nasal mucosa and the brain, toxic chemicals that are present in the air we breathe are able to have direct access to our brain and the rest of our nervous system, when we breathe through our noses.

Therefore, we need to be on guard and protect our health by avoiding situations where we will be inhaling toxic chemicals. For example, wherever possible, it would be prudent to remove yourself from exposure to scented products, pesticides, strong chemical cleansers (both household and industrial), diesel fumes, cigarette smoke, burning plastic, solvents, and so on.

Especially be on guard against products that contain neurotoxins. There are a great many consumer products that contain neurotoxins. For example, many pesticides (insecticides, herbicides, fungicides and so on) are neurotoxins. It would be very prudent to protect yourself from inhaling these toxins. They may be considered convenient, but they are poison to the nervous system. Inhaling air that contains neurotoxins will successfully deliver these poisons directly to their intended target – the brain and the entire nervous system.​