TWO chemicals found in two popular vaping flavours could destroy lung function, experts have warned.

Inhaling the e-cig liquids could increase a vaper's risk of respiratory diseases, their findings suggest.

The chemicals stop the cilia in the airways from working properly, Harvard scientists found.

Cilia are the tiny hairs that line our airways and move in a beating motion to keep the airways clear of mucus and dirt, allowing us to breathe easily.

Poor cilia function has been linked to lung diseases like chronic obstructive pulmonary disease (COPD) and asthma.

The two offending flavours are popcorn and caramel flavoured liquids, according to the Harvard study.

Popcorn flavoured e-cig liquid is especially harmful, thanks to the chemical diacetyl.

Diacetyle is used as a flavouring agent in things like butter-flavoured microwave popcorn and sweets, and although it's a safe flavouring to eat, it's dangerous to inhale.

It's been linked to a condition called obliterative bronchiolitis, dubbed "popcorn lung" because of the high levels of disease found in workers from factories that used the chemical in microwave popcorn.

Because of that risk, manufacturers have sometimes used another chemical - 2,3-pentanedione - instead.

2,3-pentanedione is used to make various things, including beer. In e-cigs, it's used to make vape taste like caramel.

But scientists claim that 2,3-pentanedione is equally as dangerous as diacetyle.

They exposed normal human bronchial epithelial (NHBE) cells to the chemicals for 24 hours.

They found that both diacetyl and 2,3-pentanedione were linked with changes in gene expression that could impair both the production and function of cilia.

Even low levels of both chemicals destroyed the cilia - suggesting that the current standards for safe limits are too low for people who work with them.

There aren't actually and standards for e-cig users, the report's authors say.

"E-cigarette users are heating and inhaling flavouring chemicals that were never tested for inhalation safety," said Joseph Allen, associate professor of environmental genetics and pathophysiology, and co-author of the study.

"Although some e-cig manufacturers are stating that they do not use diacetyl or 2,3-pentandione, it begs an important question--what chemicals, then, are they using for flavouring?

"Further, workers receive warnings about the dangers of inhaling flavouring chemicals. Why aren't e-cig users receiving the same warnings?"

Although chemicals used to flavour e-cigs are frequently used, we don't really know how they might impact our health.

But scientists from the Harvard T.H. Chan School of Public Health suggest that actually, they have a really harmful effect.

Cilia keep our airwards clear of mucus and dirt, and allow us to breathe easily.