Microcurrent therapy has what main effect on the body?

Microcurrent therapy is primarily known for its ability to stimulate blood circulation within the body. This therapy utilizes low-level electrical currents to mimic the body's natural electrical impulses, which can significantly improve blood flow. Enhanced circulation leads to better oxygen and nutrient delivery to the cells, promoting healing and rejuvenation. This improved blood flow can also aid in the removal of toxins and waste products from the tissue, contributing to overall skin health and vitality.

The other options, while they may be relevant to various skin or body treatments, do not accurately reflect the primary effect of microcurrent therapy. For instance, increasing product sensitivity and lightening skin tone relate more to specific topical treatments or treatments targeting pigmentation concerns, which are distinct from the physiological effects provided by microcurrent. Similarly, enhancing tanning is not a focus of microcurrent therapy, as it does not interact with melanin production or skin pigmentation in the same way as sun exposure or tanning products. Hence, the correct choice emphasizes the fundamental benefit of microcurrents in promoting blood circulation.