What type of reaction does iontophoresis primarily produce on the skin?

Iontophoresis primarily produces an acidic reaction on the skin. This is due to the ionization of the active ingredients used during the treatment and the physiological response they incite in the skin.

When an iontophoresis machine applies a positive or negative electrical charge to the skin, it encourages the penetration of ionized substances into the dermis. For instance, when negatively charged ions (like certain acids or anions) are used, they create an acidic environment on the skin. This acidic condition can promote various skin benefits, such as enhancing hydration, improving skin texture, or even aiding in the treatment of acne due to its effects on the skin’s pH level.

In contrast, alkaline reactions would result from using positively charged ions, which is not the primary focus of iontophoresis. Neutral reactions typically do not provide significant therapeutic benefits for skin conditions, and oxidative reactions do not specifically apply within the context of iontophoresis' primary purpose and outcomes. Thus, the correct answer reflects the fundamental understanding of how iontophoresis affects the skin through an acidic response.