Sadly, not all products marked as containing SPF can actually protect you from the sun. As well as UVB protection look for decent UVA protection from ingredients such as titanium dioxide, zinc oxide or avobenzone, non of which can be found in Blistex products.
May cause dryness
A few ingredients found in most Blistex treatments may actually cause dryness or irritation, these include fragrances and flavoring additives, camphor, phenol, menthol. Many formulations also contain alcohol which is also drying for the lips.
from the Blistex website :
Discover What Your Lips Are Missing
Blistex was founded in 1947 as a small, family-run company in the business of developing and marketing lip care products, primarily in the United States. Our objectives in those days were to create quality products, achieve consistent growth and become an innovative leader in lip care.
The pursuit of quality and customer service led us in 1967 to create our research and development facilities, as well as build our own manufacturing and corporate headquarters complex in Oak Brook, Illinois. This move enabled us to have pinpoint control of every phase of our business from product formulation and testing to manufacturing and marketing.
Over the years, consistent growth was fueled by constant innovation in the Blistex product line. New products were added and existing products improved as Blistex moved into worldwide lip and health care markets.