What is the difference between fashions in the 1970s and the fashions in the 1980s?

The difference was the 1970's fashion trends were still similar to the 1960's trends (the "British Invasion" and "Flower Child" Hippie looks), while the late seventies' and eighties' fashions changed to include a 'rainbow' of new fashion statements. Many of which were influenced by Disco dancing and movies about Disco dancing.

Women in the 1980's started wearing "BIG" hair styles. While in the 1970's hairstyles for women tended to still be more natural, as in the 1960's and "Hippie" styles. In the 80's, the new trend for men's hairstyles was the "why-did-they-do-that?" mullet. See the link on this page to the Rate My Mullet web site for photo examples. Even some women adopted that style of hair once it became popular. As the eighties progressed, women's hair continued to get bigger and stiffer and men's hair started to trend toward shorter and slicked back with gels like the characters in "Wall Street", at least the ones who could wean themselves from the mullet (that has taken decades for some, however).

1980's pants for both sexes were trending toward being worn really tight and close at the ankles instead of the Hippie and 1970-style bell bottom jeans. Baggy sweatshirts for women, cut to open the neck and worn off the shoulder like in the movie Flash Dance were popular, as were the leg warmers from the same influence in the '80's. The leg warmers were worn in summer as well as winter over the tight pants legs or with mini skirts. Women used scrunchies in their hair (often to match the leg warmers), and wore them on their wrists to "keep track of them for use later". Boy George was a fashion icon for both sexes in the mid to late 80's, too.

Men often dressed in brightly colored polyester leisure suits, many with vests for a three piece suit look, with platform shoes, like John Travolta's character in Saturday Night Fever, starting with the big Disco dancing trend in the 1980's. Or, instead, they wore "left-over hippie clothes" from the 60's and 70's with long hair, ripped jeans, and those plaid flannel "lumber jack" shirts.

But, all that said, generally speaking, the style in the 80's was more 'polyester', while in the 70's it was overall more 'natural'.