The WHO offers a rule that needs no app: the shadow rule. When your shadow is shorter than you are tall, the sun is high in the sky and its UV rays are at their strongest, so it's time to seek shade, cover up and put on sunscreen. In summer, that covers the whole middle of the day. And on hazy days, a good share of UV still gets through the clouds.
Chlorine on its own is fairly gentle. But when it combines with urine, sweat and other grime from swimmers, it forms chloramines, which cause stinging eyes and that classic 'chlorine smell'. A well-kept pool barely smells at all. Shower before you swim and never pee in the water.
Muscle mass slowly shrinks with age, putting independence at risk. But in 1990, a study had nursing home residents aged 86 to 96 train their legs for eight weeks: their strength more than doubled. Muscle responds to training at any age. Getting up from a chair without using your hands is already an exercise.