I don't think it's a new thing.
I'm 40 and I had a bath every night as a child and always have done as an adult although I now prefer showers.
I think ‘new’ is relative. I’m in my 50’s and showered every day as far back as I can remember. Not sure what happened when I was a baby/young child though.
My parents certainly didn’t shower daily when they were younger as I constantly heard how lucky we were because as kids/young adults they both had an outside bathroom that had been ‘tacked’ on to their houses at some point so you had to walk out of the house and to the bathroom. It meant it was a hassle. Hot water systems took ages to heat back then too so if there were a few people in line only the first two would have had hot/warm water. I actually lived in one of these houses as a uni student, had a daily shower but admit it was often on getting home as it was too chilly in the morning. As was common with those houses laundries were also tacked on with a room built around the existing outside concrete tubs. The place I lived in had an old tree stump in it. Tree had been cut down, stump left, concreted around and room built around it all and tacked to back of house
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None of my grandparents showered/bathed daily. When young it was once a week generally before church when a portable bath was carried in, filled up and everyone used the same water starting with the father, then mother down to youngest child with as many kids sharing as possible. Then came the miracle of the outside bathroom after the war from memory, still not daily, maybe once a week? I remember once my nanna got something in her hair. Rather than jump in the shower (now they had a regular indoor bathroom) she gave her hair a quick scrub with a bar of soap over the laundry tub. I asked why she didn’t use the shower and she looked at me like I was mad. Obviously not shower day
. People of that age were just not used to having easy access to washing facilities.
Point is no one in my grandparents generation died or suffered from lack of a daily shower/bath. My parents coped as kids/young adults, again no death, sickness, skin diseases or infections. As someone above pointed out, in general they all did more physical work than most of us do now. We have become very precious about these things.