Magnetic resonance imaging (MRI) uses a very strong magnetic field, much stronger than that produced by household magnets, but MRI has no direct effect on the health of patients (MRI as a diagnostic tool may have an indirect effect). The iron concentration in our blood is too low to be affected by the weak magnetic field of household magnets. In addition, the iron atoms in our blood are bound in heme molecules. The chemical bond that fixes the iron atom in the heme molecule interferes with its electronic state, causing the iron atom to lose its normal ferromagnetism.
Controlled experiments have repeatedly determined the lack of healing properties of magnets. For example, MS Cepeda and colleagues found that static magnetic fields had no effect on pain levels. A study conducted by MH Pittler that reviewed multiple experiments also confirmed that magnets cannot heal. Indeed, all materials (including oxygen and frogs) have some kind of magnetic response. The problem is that a very strong magnetic field is needed to make this response significant. Household magnets, and even MRI, are too weak to have any lasting effects on humans. The strong magnetic field of MRI is used to temporarily redirect the magnetic dipoles of protons in the body for imaging. After alignment, protons quickly become misaligned due to natural heat and biological movement, and the rate at which they become misaligned can be used to image different tissues.
If a person is exposed to a static magnetic field sufficient to produce a significant effect, the result will be harmful, not cured. Blood can accumulate where it shouldn't be, and it can even explode from blood vessels. Please note that we are talking about static fields here, such as those generated by permanent magnets. Changing the magnetic field can have a significant impact, but once the magnetic field starts to change, it is no longer just a magnetic field. It becomes an electromagnetic field. Electromagnetic fields only affect biological tissues when they are very strong (for example, the sun burns you or laser cuts your eyes) or high frequency (for example, X-rays make you cancer). In any case, the handheld permanent magnet will only generate a static magnetic field, not an electromagnetic field.