Sunlight is bad. It is a source of UV radiation which releases free radicals in your skin which damage the collagen in your skin which is why the skin on parts of your body exposed more often to the sun look older. It is a good idea to be liberal with the sunscreen as a rule. And it might sound like it is a good idea to seek out products that contain UV filters. A lip balm with sunscreen for example.
The logic is faultless, but ignores the fact that the UV filters can have other effects. The upper level of the skin, known as the stratum corneum, is the body’s barrier that prevents stuff outside getting in. It also regulates the loss of moisture from the body. It does these two jobs remarkably effectively. The trick is that it has oils that have a very particular structure – a liquid crystal structure. This is pretty resistant to most things that might disrupt it. But it can be upset by things that are almost but not quite the right shape. Imagine a wedge shaped piece of wood nearly the same size as a Jenga piece. It would play havoc with the game.
Unfortunately UV filters can have this effect on the liquid crystals in the skin sometimes. This is not too bad a problem in the kinds of formulations used for sunscreens which get spread fairly widely and thinly. But in lip balms which by their nature get applied in much thicker layers and which are frequently reapplied it can be quite damaging for some people. I wasn’t surprised to see that this has been picked up by the media in the US recently.
The moral of the story is that if you are using a lip balm for chapped lips that doesn’t seem to be working check the ingredient list. If it contains a benzophenone – they are listed as benzophenone-1, benzophenone-2 etc up to 12 – it might be worth looking for another choice.