E-cigarettes have long been a subject of debate on whether or not the product doesn't bring health hazards. Now, a new study finds that the chemicals in e-cigarette flavors can cause a certain lung disease.

The study, conducted by researchers from Harvard T.H. Chan School of Public Health, found that e-cigarette flavors mostly contain the chemical called diacetyl, which is known to cause "severe respiratory diseases," as stated in the school's Harvard Gazette.

Published last Tuesday, the study specifically found that over 75 percent of the tested e-cigarette flavors and refills contain the aforementioned chemical.

To arrive at the findings, lead author Joseph Allen and a team of researchers investigated 51 different types of e-cigarette flavoring and liquids from popular brands.

The researchers tested for the presence of acetoin, 2, 3-pentanedione and diacetyl. The study then found that in 47 of the 51 tested flavors, there's at least one out of the three chemicals that was present.

Diacetyl was present at levels beyond the laboratory limit in 39 of the flavors, acetoin in 46 flavors, and 2,3-pentanedione in 23 flavors.

Study co-author David Christiani said in the news release that there are a lot of things that remain unknown about e-cigarettes. Most health concerns are targeted on the nicotine levels of e-cigarettes but the levels of cancer-causing chemicals usually go unnoticed, according to Christiani.

The researchers also highlighted that the chemicals present in e-cigs and their flavors are those that can contribute to a disease commonly known as "popcorn lung" or in its scientific term, bronchiolitis obliterans.

This disease was first observed among workers in microwavable popcorn manufacturing plants who are exposed to the scent of artificial butter flavor. But Allen said that diacetyl and other related chemicals were not only detected in artificial butter flavor but also in different flavorings, including alcohol, fruit flavors, and candy flavors, which are used in e-cigarettes.

Researchers added that the chemicals in e-cigarettes undergo heating and vaporization before inhaled, and this likely puts the smoker at the same level of exposure as the workers in the microwavable popcorn facilities, according to the Wall Street Journal.

Detailed findings of the study were published in Environmental Health Perspectives.