Salt lamps, which are merely light bulbs of varying wattages placed within blocks of rock salt of varying sizes, have become an increasingly popular product in the alternative medicine scene and are marketed as “natural ionizers.” An ionizer, in theory, produces ions, which are atoms or molecules with a net positive or negative charge caused by an uneven number of protons to electrons.
According a popular (and representative) Facebook post about salt lamps, the product can positively affect your health in these diverse ways:
- They emit “boundless amounts” of negative ions, which counter the positive ions that both surround us and make us feel bad.
- Those ions increase oxygen flow to the brain which combats lethargy, gives you more energy, and causes you to be more alert and responsive to your surroundings.
- The ions negate the “radioactive waves” or “electric smog” emitted by our electrical devices.
- The ions offer protection from airborne toxins that could be floating around us.
- The constant intake of negative ions makes your slumber less fitful, and helps you get more out of your rest.
- The ions lower high blood pressure, reducing the chance of heart attacks and strokes.
- The salt that is used in these lamps, Himalayan salt, contains up to 84 trace minerals that your body needs, allowing the lamp to also strengthen your bone, regulate your body pH, and balance the water content in your body.
All the claims described above rely on the singularly false assertion that a block of salt with a light bulb inserted inside will naturally emit negative ions. That argument, when intelligible, usually invokes some sort of interplay between the salt, which attracts water from the air, and the heat from the light evaporating that water, as described in a non-peer-reviewed 2010 paper in the Pakistan Journal of Molecular Biology:
The negative ions are generated by a continuous interplay of water attraction and evaporation. The salt crystal lamp attracts water molecules from the surrounding air to its warm surface. The water and salt form a solution. In the process of evaporation of the solution, due to the heat of the lamp, negatively charged ions are created. Both positive and negative ions are created but much more negative ions than positive ions are created, therefore providing a surplus of negative ions. Natrium [another word for sodium] is positively charged. This unique ion emission interplay ability with water is because of salt’s neutral atomic structure.
This explanation has the great benefit of sounding scientific. Who really knows how ions are formed in the first place or what will happen to blocks of heated salt rock, anyway? One person with pretty deep knowledge on the topic is Caltech professor of chemistry Jack Beauchamp, an expert in (among other things) the myriad processes that generate ions and the analytical methods used to detect those ions.
Beauchamp was skeptical that a heated block of sodium chloride would produce ions (any amount of them, positive or negative ones, let alone “boundless amounts”) but not so skeptical that he didn’t want to hook up the most popular salt lamp available from Amazon.com to his lab’s quadrupole ion trap mass spectrometer. This instrument, in essence, sucks in air from directly around the solid and analyzes the mass and charge of particles captured by the instrument. Here’s Beauchamp description of what he did in his own words:
We have a lot of experience with observing ions. What we did with the lamp, since it's supposed to make negative ions, was to place it adjacent to the inlet and, just by itself, we observed no ions at all. We turned it on and looked for negative ions. We looked for positive ions. We waited for the lamp to heat up. The bulb inside eventually does heat the rock salt, but we didn't see anything.
I can't think of any physical process that would result in the formation of Ions from heating rock salt, with and without the presence of water vapor in any amount. Rock salt has a face-centered cubic structure which would not be expected give rise to electric fields that would generate ions around individual crystals.
The structure aspect is important, says Beauchamp. One way to get crystals to generate ions is to alter the shape of its crystal structure via temperature, something that can happen if a crystal structure is asymmetric. He points to a crystal called lithium tantalate, which changes its crystal structure when heated up in such a way as to create areas of high and low electrical potential when heated or cooled. This property allows it to generate an electric field that could, in theory, ionize the air around it. Sodium chloride’s chemical structure is a symmetrical cube that does not have the capability to generate high electric fields in the vicinity of a crystal.
The bottom line, according to Beauchamp and other chemists, is that there is no reason why putting a 15–45 watt bulb in a block of sodium chloride would do anything to generate ions, and this suspicion was confirmed by testing one of the most popular salt lamp models on the market with a machine designed specifically to detect ion formation.
However, since one should always be concerned with low-sample, un-peer reviewed research (as our salt lamp experiment undoubtedly was), it is worthwhile looking into the claims that rely on salt lamps' producing the ions we could not find, as these are equally tenuous in their scientific validity.
They emit “boundless amounts” of negative ions, which counter the positive ions that both surround us and make us feel bad.
As discussed above, “boundless amounts” of negative ions would be a bit of a stretch, given the total and complete lack of any ions generated by our lamp. Ignoring that fact, however, brings us to the claim that positive ions make us feel bad and negative ions make us feel great. In terms of effects on mood, there is some research that suggests that negative ions can play a role in the treatment of seasonal affective disorder. A 1998 study in JAMA psychiatry found, for example, that:
Bright light and high-density negative air ionization both appear to act as specific antidepressants in patients with seasonal affective disorder. Whether clinical improvement would be further enhanced by their use in combination, or as adjuvants to medication, awaits investigation.
A similar 2006 study, published in the American Journal of Psychiatry, hinted at at the possibility that high concentrations of negative ions could aid in the treatment of seasonal affective disorder. A 2013 review concluded, more broadly, that negative ions at very high concentrations had an effect on improving mood.
These studies, however, used high concentrations of negative ions generated by industrial scale ion generators. Seeing as we have uncovered no evidence to support the claim a salt lamp produces any ions, the notion that a $29.99 block of rock with a light bulb could rival the power of a specifically designed laboratory equipment seems dubious. Much of the pseudoscience written about the positive effects of negative ions similarly disregards scale in their analyses, equating negative ionization at any level as the same phenomenon.
Those ions increase oxygen flow to the brain, which combats lethargy, gives you more energy, and causes you to be more alert and responsive to your surroundings.
There are two main arguments one could make to suggest negative ions increase oxygen flow to the brain or provide you with more energy. The first one is that negative ions increase respiratory function and, as a consequence, would allow your body to deliver more oxygen overall. This claim, though oft repeated, has very little evidence to support it. A 2013 systematic review of papers investigating a relationship between exposure to ions and respiratory health stated:
Despite numerous experimental and analytical differences across studies, the literature does not clearly support a beneficial role in exposure to negative air ions and respiratory function or asthmatic symptom alleviation. Further, collectively, the human experimental studies do not indicate a significant detrimental effect of exposure to positive air ions on respiratory measures. Exposure to negative or positive air ions does not appear to play an appreciable role in respiratory function.
The other claim, discussed in more detail below, has to do with a study published on the effects of ionization in neural structures and blood flow in laboratory rats. In a similar issue of blindly comparing different scales, these rats (which are both not human and much smaller than humans) were directly fed negatively ionized air at high concentrations that would be inconceivable for a block of salt to produce, even if it did produce some small amount of ions.
The ions negate the radioactive waves or “electric smog” emitted by our electrical devices.
While “radioactive waves” are not—strictly speaking—a thing, what the author is likely talking about is an electromagnetic field generated by household electronics. The issue is that the only problem a salt lamp (via its dubious negative ionizer mechanism) would theoretically solve is a preponderance of positively charged ions in the air which would be in turn neutralized by the negative ions. An electromagnetic field will only generate ions if the voltage is high enough to cause an electric discharge, and the electromagnetic fields generated by household appliances are not that that strong, per the WHO:
Some electromagnetic waves carry so much energy per quantum that they have the ability to break bonds between molecules. In the electromagnetic spectrum, gamma rays given off by radioactive materials, cosmic rays and X-rays carry this property and are called 'ionizing radiation'. Fields whose quanta are insufficient to break molecular bonds are called 'non-ionizing radiation'. Man-made sources of electromagnetic fields that form a major part of industrialized life — electricity, microwaves and radiofrequency fields — are found at the relatively long wavelength and low frequency end of the electromagnetic spectrum and their quanta are unable to break chemical bonds.
In terms of lessening the actual voltage of any electromagnetic field caused by household electronics, you’d be hard pressed to come up with a mechanism by which a salt lamp could provide any effect whatsoever, even if it did produce “boundless amounts” of negative ions.
The ions protect you from airborne toxins that could be floating around us.
Many air filters do have an ionization component to aid in the removal of dust and particulate matter from the air. These machines ionize the air, then attract the dust and other ions created with charged surfaces as air is pushed through the system, thus and removing those particles from the air.
A block of sodium chloride, which, again, does not produce any ions, does not have any mechanism for the flow of air or the trapping of the particles in that air, and would therefore be useless as an air filtration system. This is, incidentally, why the Sharper Image Ionic Breeze line of products, despite actually producing ions, is complete bunk.
The constant intake of negative ions makes your slumber less fitful, and helps you get more out of your rest.
This claim has existed sporadically in the scientific literature for decades, but ultimately is not supported by current science. A 2013 review of psychological effects attributed to air ions, which looked at 33 studies from 1957 to 2012 evaluating “the effects of air ionization on depression, anxiety, mood states, and subjective feelings of mental well-being”, concluded:
No consistent influence of positive or negative air ionization on anxiety, mood, relaxation, sleep, and personal comfort measures was observed.
The ions lower high blood pressure, reducing the chance of heart attacks and strokes.
This claim stems from research performed on laboratory rats who were under anesthesia and essentially pumped directly with high concentrations of negatively ionized air. It goes without saying that humans are not rats, and a that specifically designed laboratory ionization instruments produce a whole lot more ions than a salt lamp, which, not to drive this point home too much, they do not.
The salt that is used in these lamps, Himalayan salt, contains up to 84 trace minerals that your body needs, allowing the lamp to also strengthen your bone, regulates your body pH, and balances the water content in your body.
This assertion is perplexing because it is a) unclear where that number comes from, b) which ones they are, or c) how these trace minerals would be released from the salt in a lamp and transported into your body.
It seems likely that the number and associated health claims comes from a page on Dr. Mercola’s online store in which he is selling his own brand of Himalayan salt (supplies are limited!) Ironically, Mercola claims Himalayan salt to be “the most pure” while simultaneously suggesting its health benefits come from its impurities:
This salt from the Himalayas is known as "white gold." Together with pure spring water, Himalayan Crystal Salt offers all the natural elements original to its source – the very same elements originally found existing in the "primal sea."
Containing at least 84 naturally occurring trace elements in their natural mineral form, the benefits of natural Himalayan Crystal Salt include [...]
Needless to say, the claims listed on an advertisement for a product cannot be taken as peer-reviewed science. Not that you need to even look that far.
This advertisement is for salt to cook with, which would provide a much more plausible route for those trace minerals to get into your body. Unless you are licking your salt lamp, however, the only thing those impurities might do is impart its nice pinkish color.
Incidentally, that nice pinkish color that glows once the bulb is turned on is the only thing you are going to get from a salt lamp. Salt lamps may look neat, but claims that they can do anything medically rely — fatally — on the claim that the lamps produce negative ions and then further rely on a series gross simplifications or misinterpretations of science to argue that those negative ions (which don’t exist in the first place) could affect you in any meaningful way.