As more consumers become aware of the environmental and human costs of apparel production, fewer will opt for fast fashion, widely seen as the most problematic sector in the industry, according to a report Monday from investment firm UBS.

Fast-fashion retailers could face revenue declines of 10% to 30% over the next five to 10 years, the analysts said in an emailed report.

"The compounding effect of consumers buying fewer items but also shifting the purchases they do continue to make to items that they perceive to be more sustainable could be severe," UBS Analyst Victoria Kalb's team wrote.

Apparel companies, including fast fashion, are increasingly addressing rising consumer concerns. H&M in particular is experimenting with textiles and releasing eco-minded collections. But siloed efforts may not be enough to ward off rejection of the idea of disposable clothing.

"Whether the garment is conventionally produced with a significant environmental footprint, the cotton used in a t-shirt is organic, the polyester in a fleece is recycled, or the garment or shoe is vegan (which, incidentally, often means plastic) becomes largely insignificant when set against the sheer quantity of items produced and discarded," according to the UBS analysts.

Instead, apparel companies need to slow down and reduce their output — an idea antithetical to the production and supply chain methods honed by fast fashion in the past several decades. "System redesign is required (fewer items sold, items lasting longer, fewer items disposed of, achieving circularity), rather than replacing conventional garments with 'more sustainable' alternatives," UBS said.

Measuring consumer sentiment, particularly changes in that sentiment, is extremely difficult, and especially so in a sector as intrinsically volatile as fashion, the analysts noted. But they also said consumers are increasingly exposed to educational and marketing campaigns about climate change and the environment, and that even local governments are taking steps in areas like waste management, chemical pollution and water management.

In a survey of consumers in the U.S., U.K. and Germany, UBS found that more than half are aware of people who have changed their shopping behavior over environmental concerns. And they found a willingness to change, in that while 58% said they were previously unaware of apparel's environmental impact, 20% to 25% of those consumers would buy less clothing now that they are, and 28% to 31% said they'd "seek out sustainably manufactured clothing."

The report comes on the heels of similar analysis from Moody's Investors Service last week that fast fashion and discount brands will likely face the most competition as environmental and social issues carry more weight in purchasing decisions. Moody's also noted that apparel companies seen as bad for the environment face "reputational risk."

UBS analysts likewise see "public pressure campaigns" as effective in stoking "strong feelings (or embarrassment in the context of public opinion)," which in turn results in "a fundamental change of habits." Moreover, such sentiment can hit a tipping point, as when perception of sugary soft drinks deteriorated to the point where sales declined 24% over two years. "While we do think companies have options in responding to these shifts ... we see changes in consumer behaviour as being more powerful than companies' ability to respond," UBS warned.