The humidity and heat of summer affect your skin and body in many ways. They cause water loss from the body (leading to dehydration), which can be seen on the skin too. They make our oil glands more active, which means you may end up with more sebum around the t-zone than you are used to. This increased oil flow in addition to the constant application of sun protection can lead to breakouts, since the skin can become easily congested.
In short, summer can be unforgiving to our skin, to not mention what we put our skin through ourselves - sun baking, tanning, sunburns, excessive sun exposure, heat, air conditioning, alcohol, lifestyle, and pollution.
So not only make sure to hydrate your skin and keep adequate water intake, but also re-evaluate your skincare routine to address this change in conditions.