The best advice for how to dress in Peru is to dress in layers. The mornings and evenings can be very cold, but it can get very hot in the afternoons so you need to be able to shed a layer or two as the day heats up. Layers should be easy to carry with you if you’re not planning to stop back at your accommodations during the day to drop off jackets or change, so lightweight and comfortable fabrics are key. Be sure you are always prepared for the rain, as well, especially if hiking. Lightweight long pants and long sleeves will also come in very handy to ward off mosquito bites.
Peru’s cities have some very nice restaurants and a vibrant nightlife that you may feel like dressing up a little bit for. While you don’t need to dress super fancy, it’s worth packing a couple of smart-casual outfits for the evenings and maybe some inexpensive jewelry.
When visiting one of Peru’s many religious sites it is strongly advised that you dress conservatively and cover up shoulders or bare legs if possible. Swimwear should be reserved for the beach and poolside only.