Here's why:

* pH measures the acidity or alkalinity of a solution. Sunscreen is a cream or lotion, not a solution.

* Sunscreens are formulated with a variety of ingredients, including UV filters, emollients, and preservatives. These ingredients interact with each other and the skin, making a simple pH measurement meaningless.

* The effectiveness of sunscreen is not determined by its pH. The primary function of sunscreen is to absorb or reflect UV radiation, which is independent of pH.

Instead of pH, sunscreen effectiveness is measured by its SPF (Sun Protection Factor) and its ability to block both UVA and UVB rays.

Let me know if you have any other questions about sunscreen.