Bathing nude in a bathtub or in a shower is not called skinny-dipping, but bathing nude in a hot tub or hot spring sometimes is. A variant of skinny dipping is skinny diving, which is diving (underwater) naked.
Historically, all swimming was skinny-dipping until the first swimsuits were invented in the mid-19th century. By the year 1900, the situation had turned into its opposite in the western world: nude swimming in public places was considered offensive, made illegal, and everyone would wear long swimming costumes. For a decade or two it was even forbidden for males to swim topless.
By the mid-20th century, males would wear swimming trunks that covered no more of the body than shorts or briefs, and females would wear swimming suits that covered most of the torso. The head was typically covered with a swimming cap. In the 1960s, the bikini came into fashion, as well as toplessness for females in some cultures. In the 1990s, occasionally one could see swimwear in thong style that exposed the buttocks.
All the while though, skinny dipping coexisted with swimwear. Nude swimming remained particularly common for children in rural areas, and swimming classes for boys, where no females were present, were often held naked as it was seen as more practical.
In many parts of Asia, skinny dipping for prepubescent boys remains common to the present day, whereas girls are rarely seen in such activities.
Today, many countries have laws that forbid public nudity, including skinny dipping. Cultures that tend to be particularly troubled by nudity in these days include the United States and islamic, in some part also catholic countries, although there are exceptions. In many places, skinny dipping today is only possible in privacy or secrecy if one wants to avoid negative consequences, e.g. in remote (or private) lakes, rivers, pools, beaches, or at night time where one is unlikely to be seen.
The subject of skinny dipping, sometimes as an innocent fun and sometimes with erotic connotations, especially when done secretly/nightly by teenagers or adults of opposite sex together, is often featured in popular culture, for example in various movies and even in some songs.
In most of Europe, skinny dipping of toddlers and small children in outdoor public places remains accepted and common today, while it is not so common in indoor public places, and neither accepted nor common for teenagers and adults. Toplessness of women is accepted in many outdoor public places, but not full nudity. There are however specific designated nudist places where full nudity is not only permitted but often mandatory for everyone, including adults. Public nudity in designated places is becoming more popular since the 1960s/80s as part of the wellness trend (combined with other trends such as sauna, steam baths, solariums, massages, etc.). Some spas today, for example in Germany, are "textile-free" on certain days or at certain hours, which means in those periods swimwear is not allowed. People are permitted to cover their bodies with towels and bathrobes though, as long as they don't wear swimwear and are naked in the water.
In places where skinny-dipping is forbidden, such as non-nudist lakes, pools, water parks and beaches, children who do so may be subject to punishment by their parents (and above a certain age, also by officials and/or the state).
Skinny-dipping is sometimes featured as an offense in spanking fiction, e.g. in Pepper Tree Lake. Naturally it makes for interesting scenarios, with elements such as nudity, innocence, wantonness, embarrassment, shame, bare bottom spanking, wet bottom spanking, etc.