"In addition to longer daylight hours and more intense sunlight giving rise to greater UV exposure, summer also sees us being subject to higher average temperature.
Heat is known to kick our sebaceous (oil) glands into overdrive. As a result, our skin is generally oilier in summer. The oil produced by our skin, sebum, probably served an important function during the earlier part of our evolution when we were furry in waterproofing our hair and skin (important when roaming naked without the benefits of Goretex). Its dubious if sebum had retained any purpose as we evolved; babies and young children do very well with their non oily skin.
We know for a fact that excessive oil production predisposes us to whiteheads, blackheads and breakouts. Sebum is also known to be pro-inflammatory and conditions like acne and rosacea are associated with oily skin.
Good skin care in summer is therefore important in maintaining skin health and avoiding the oily/shiny look. We recommend the use of a good cleanser like Environ Sebuwash and ZO Offects Exfoliating Cleanser twice daily, spending up to 1 minute each time, and a toner to adequately control the oil production before using your usual skin care products. And use sunscreen."