Basically what this claim does is take a known phenomenon and assign it a significance it does not deserve.
Copper staining occurs as a result of oxidation of the bracelet in response to exposure to many factors, not just the body. To understand this all it takes is to look at the basic reaction which is occurring, and the factors which affect it.
There is no basis for assigning any particular significance to this staining process.
Even if we were to ignore the fact that copper interacts with environmental oxygen and assume that the major reactant in staining is sweat or other metabolic waste products excreted through the skin or sebum, sweat is generally not a reliable indicator of any specific disease state or metabolic process (though exceptions can be made for cystic fibrosis, certain genetic disorders, and some cases of poisoning). It is difficult to discern medically relevant data from sweat even when subjected to chemical analysis, and what can be gained is generally limited to specific conditions. Even then, samples cannot be considered accurate unless they have an adequate volume. To assert that any valid assessment of anything can be done by randomly determining the color of a stain caused by a very tiny amount of sweat and limited skin contact in an uncontrolled environment is ridiculous.
Sweat is actually quite a complex thing (for this discussion I am lumping anything you can excrete through the skin as sweat). It is composed of sodium, potassium, calcium, magnesium, fatty acids, amino acids, chloride ions, and many other things which can all react to solubilize copper and cause a stain. However, there is no credible evidence that any of these levels are significantly altered in any particular condition.
It is also normal for the chemical composition and pH of sweat to vary within a certain dynamic range, as well as that of the skin, sebum and acid mantle. Even fluctuation within this range can change the outcome of the staining without indicating any "illness"
Also, basic chemistry tells us that there are other variables in this reaction, most of which have nothing to do with metabolism or illness, and therefore would confound any attempt to derive accurate health information from interpreting the stain.
- Soaps used
- Length of reaction
- Temperature at which reaction occurs. Obviously, heat will speed up this reaction, changing the properties of the stain.
- Frequency of bathing/showering
- Specific chemical properties of water which the skin or the bracelet may be exposed to. Which includes regional variations in water quality, use of well water, acidity of local rainfall.
- Chemical composition of the bracelet itself.
- Environmental oxygen
The idea that solutions containing copper can be absorbed transdermally and may have anti-inflammatory properties is based on actual science.
However, the chemical formulations are very particular and not without side effects of their own and similar effects cannot be achieved by simply wearing copper jewelry.