Thanks for the info. So it's pretty essential for a few weeks a year, and then you can stick it in the cupboard for next time.
It depends on what you do and what you wear. I think it was last summer or the one before that when I was doing gardening in the back yard one sunny day in June for a couple of hours. The day was quite warm although not hot but because I was shoveling dirt and carrying heavy bags, it felt hot and I took off my shirt. That was a mistake. The first night was very uncomfortable. My wife had to apply some lotion onto my back to ease the pain. It got easier but my skin was peeling for a over a week after that.
When I was a kid I remember getting a bad sunburn a once or twice.
I've never owned anything over factor 30, but try not to spend more than an hour in the sun in the summer - in Spain that is, UK is no cream bar face :)
I can manage without sunscreen at home from mid May to late August but only if I keep my shirt on.