Sunlight sensitivity is a side effect of some treatments for ALK+ lung cancer (specifically Alectinib).
Sunlight sensitivity means that your skin is more susceptible to burning easily. Even 15 minutes of exposure may be enough to start a sunburn.
Even when your skin does not appear burnt, it can feel irritated in hot (or warm) water.
Skin protection is essential when you're on a medication that can cause sunlight sensitivity. This includes ALL skin including hands, feet, face, lips, nose, back of your neck, etc. Even being exposed to the sun through a car window can cause a burn. So consider protection anytime you're exposed to the sun.