The only way to severely burnt hair is by trimming. Prevention is the safest plan. Frizzy hair is often the result of too much sun time. Hanging out in the sun without protection for your hair and scalp is the worst thing you can do. Use leave in hair products with SPF protection when you know you will be at the beach is you are unwilling to wear a hat or a cover-up.
Hair needs to be treated more gently during the summer.
Consider switching to a more moisturizing and overall gentle shampoo. Phytologie's Academia is one of their most gentle shampoos. California Baby has a very special shampoo that can be used for babies and adults. For summer months consider switching to hair care products that are as all-natural as possible. Paul Penders , Giovanni , Aubrey Organic, JR Liggitt and California Baby contain absolutely no harmful chemicals.