Your skin changes with the seasons, and what may have worked in the bonny springtime won't necessarily be effective when the humidity drops and winter starts to take its toll. In winter, not only does cold air chap and dry out skin, but you also spend much more time indoors, where the air is even drier. You may need to increase the amount of moisturizer you use.
Getting too much vitamin A in winter can also be a problem, as it's linked to decreased oil production [source: Kunin]. While this can be a boon for people with oily skin, it can also exacerbate problems with flaking and redness during cold weather. If winter makes your skin dry out, and you use a topical ointment containing vitamin A (it shows up in acne, psoriasis and skin rejuvenation products), you might want to ease up.
Wear sunscreen in the summer, even if you're not going outside. Sunscreen and products that contain UV blockers are a good idea year-round, but they're especially important in the summer when stronger rays dehydrate, wrinkle and threaten skin cancer.