As a surfer, I always try to breathe the purest sea air possible. Because of its richness in mineral salts and negative ions, sea air has many health benefits. The swell, the waves, and the winds increase the concentration of these elements. To reproduce these effects in the indoor air of my medical practice, I decided to test an ionizer device that, in addition to the expected effects on well-being, reduces the presence of microbes, micropollutants, and allergens in the indoor air that my patients breathe.
Guillaume Barucq, General practitioner and author of the books "Surf Therapy" et "Detoxification"
Where do we find negative ions?
The air is naturally ionized, balancing positive and negative ions in natural environments.
In the purest natural spaces, we can find large quantities of negative ions: at the foot of waterfalls, for example, the bursting of water droplets releases electrons (a physical phenomenon called the Lenard effect) which ionize oxygen (O2- ion, see below) or in the mountains, by the sea, in the forest, in the sun...
A short lesson in physics and chemistry:
An ion is an atom, or a molecule, which has gained or lost one or more electrons. If the atom is neutral, the ion is electrically charged. A negative ion comes from an atom that has gained one or more electrons.
The oxygen molecule O2, which makes up 20% of the air, is an electrophilic molecule that easily acquires an extra electron (in red, see drawing), to form the O2-.
Have you ever felt the calm before the storm? And why a sudden feeling of peace at the seaside? This is where ions come into play and influence our physiology.
Some studies have established that negative ions are beneficial to our health: they improve our sleep quality, our body tissue oxygenation, our concentration, and our mood... Negative ions would also make us less vulnerable to stress. 
How harmful are positive ions
The positive ions are present in polluted environments, while negative ions tend to disappear, particularly in closed spaces where the air is conditioned (i.e. heat is transferred between the air and the ceiling). Some devices can increase positive ions, such as AC, photocopiers, electronic cards, or screens.
The effects of positive ions on human health start now to be known: increased irritability, migraine crises, or even thrombosis in response to changes in the electrical charge of the atmosphere that follow meteorological upheavals. 
Researchers found that these electrical charges (aka positive ionization) generated by weather change produce a release of serotonin in our body. They also identified three types of weather sensitivity responses:
- Hyperproduction of serotonin causing a typical irritation syndrome.
- Adrenal deficiency producing a typical exhaustion syndrome.
- Hyperthyroidism with "sluggish" thyroid symptoms.
A bit of history:
According to André Van Lysebeth, who introduced yoga to the West, negative ions are one of the key vehicles of Prana in the air:
- “(...) I have the impression that I was the first to establish a correlation between certain scientific discoveries and the yogic theory of Prana. Based on Western research, conducted without any connection to yoga, I am convinced that one of the forms (if not THE main form of Prana) is constituted by free negative ions… those tiny packets of electrical energy carried by the oxygen atoms in the air, and that this energy is assimilated by our body.”
"Pranayama: the dynamics of the breath", Editions Flammarion,1971.
Negative ions at home for better indoor air quality: yes, but without ozone!
The offer of air Ionizers has increasingly developed in the category of air purifiers. No doubt that air ionization is an effective air purification technology. However, if not properly controlled, it can emit ozone. Before purchasing an air ionizer, be sure it does not emit any ozone! This gas is harmful to your health and would cancel all the benefits of negative ions.
Rest assured that TEQOYA ionizers are 100% safe. They are the only ones that do not emit ozone: independent laboratory tests that have measured ozone within a few centimeters of a TEQOYA unit report a density of less than 2 ppb, which is about as accurate as measuring devices.  TEQOYA air ionizers are also energy efficient (1.5W, or less than 5 euros per year). You can sleep tight... and breathe healthy air!