Yes, SPF is crucial after using peptides. Peptides themselves don't offer sun protection, so applying a broad-spectrum SPF will shield your skin from harmful UV rays and prevent sun damage.

Peptides are not direct sunscreens. They work to repair and strengthen skin, potentially mitigating some sun damage effects *after* exposure, but they do not block UV rays like SPF does.

Peptides themselves don't typically increase sun sensitivity. However, it's always wise to use sun protection when incorporating new skincare products, as any active ingredient can potentially cause slight irritation in some individuals, making them more vulnerable to sun damage.

Avoid mixing peptides with strong direct acids like AHAs (glycolic, lactic acid) or BHAs (salicylic acid) in the same application, as the acids can degrade the peptides and reduce their effectiveness. It is generally recommended to use them at different times of the day.