Yes, SPF is crucial when using hyaluronic acid. Hyaluronic acid hydrates the skin, making it more susceptible to sun damage. SPF protects the skin from harmful UV rays, preventing premature aging and damage.

Some dermatologists advise caution because hyaluronic acid's effectiveness depends on humidity. In dry environments, it can draw moisture from the skin instead of the air, potentially leading to dryness. Proper formulation and layering with occlusive moisturizers can mitigate this.

Avoid using hyaluronic acid in very dry environments without layering it with a heavier moisturizer or occlusive. This helps trap the hydration and prevents the hyaluronic acid from drawing moisture out of the skin itself. Also, avoid using very high concentrations without consulting a dermatologist, as it could potentially irritate sensitive skin.

The main downside is that hyaluronic acid can sometimes exacerbate dryness in low-humidity conditions. It can draw moisture from the deeper layers of the skin if there isn't enough ambient moisture to draw from the air, so proper layering with a moisturizer is key.