Hi Tara, you are right that low concentrations of Zinc Oxide might not offer sufficient sun protection but 23% should be safe. About this particular product: This product does not state any SPF label (at least I couldn't find any), so I would be very careful with that. That probably means that this brand didn't test for SPF and hence does not know the true SPF of the product. It is not safe to assume 23% zinc oxide equals XX SPF, sunscreens are more complex than that. So be careful, I would distance myself from this product.

Thank you very much!