No matter whether an English gentleman or lady believed in full into-the-tub bathing, or more cautiously followed popular medical advice and washed rather than bathed, there was one area in which both sides were in complete agreement: what they wore next to their skin was impeccably clean.
For gentlemen, a linen shirt was an all-purpose garment well into the 19th century. Whether fine Holland linen or coarse homespun, the shirt was always voluminously cut and always white. It slipped over the head and hung nearly to the knees, with buttons at the throat and the cuffs. (It's only romance cover artists who make a historical hero wear a silk tux shirt open to the waist.)
A shirt served as underwear as well as a nightshirt, and was the one "layer" that lay directly on the skin, absorbing sweat and preserving coats and waistcoats. A clean shirt was a point of pride for men of every rank. Even laboring men tried to have at least two, one to wear and one being washed. Fine gentlemen might change their shirts several times a day; some might own as many as fifty. But as long as a gentleman's shirt was clean, then he was considered clean as well.
It probably worked pretty well, too. Linen is a soft, absorbent fabric, and by the time a laundress had washed and rinsed it repeatedly with strong soap, dried it by the sun, and pressed it with steaming-hot irons, a linen shirt would have been clean and fresh-smelling enough to please even a fastidious 21st c. nose. Wealthy Londoners sent their linen to the country to be washed, in cleaner water far from the sooty air of the city.
The same thing applied to a lady's smock, shirt, or chemise; the name changes over the centuries, but the billowing square shape doesn't. It, too, was invariably white linen, though it could be trimmed with lace or discreet embroidered initials. The smock went beneath petticoats, stays or corsets, and gowns, and protected those costly pieces from sweat and dirt. (Again it's only on book covers or in Madonna videos that corsets are worn next to the skin.) Shifts were changed at least daily, and as with a man's shirt, a clean shift meant a clean lady.
Above left: Woman Doing Laundry, by Henry Robert Morland (1716-1797)