New U.S. research that smoking hookah exposes users to potentially dangerous levels of a chemical compound called acrolein, which is believed to cause cancer and heart disease.

Despite the potential dangers of hookah smoking the activity has grown in popularity in recent years, partly due to its sweeter flavored smoke which makes it particularly appealing to teens and younger adults. The smoke is generated by heating hookah tobacco that is fermented with molasses and fruits, giving it is sweet taste, and combined with burning charcoal. It then passes through a partially filled water jar and is inhaled by the user, often in bars and and at events which can make it appear more innocent than tobacco smoking.

To look into its potential dangers, a team from San Diego State University's Center for Behavioral Epidemiology and Community Health looked at levels of 3-HPMA in participants after attending an indoor hookah event.

3-HPMA is a metabolite of acrolein, a byproduct of burning hookah tobacco and a known respiratory irritant.

The team collected urine samples from 105 hookah smokers and 103 non-smokers, but who were exposed to secondhand hookah smoke.

In order to make comparisons the samples were taken the morning of the event and the morning after.

They found that after spending an average of three hours at a hookah event, the levels of 3-HPMA in urine increased by an average of nearly 1.5 times, in both those smoking hookah and those who didn't but were exposed to the secondhand smoke.

Lead author Nada Kassem also added that, "The acrolein levels were even higher in people who smoked hookah on a daily basis. They had acrolein levels four times higher than those found in a representative sample of non-tobacco users in the United States."

Kassem has already found in previous studies that hookah smoke could be potentially dangerous for health, finding that children five years or younger who live in homes of daily hookah smokers also show levels of urinary 3-HPMA 1.9 times higher than levels of than children who live in non-smokers' homes.

For her the evidence points to one conclusion: that hookah is not a safe alternative to smoking other forms of tobacco.

"Our results support regulating hookah tobacco products, including reducing additives that produce acrolein, including sugars that sweeten the smell and taste of the tobacco, and humectants, which are used to maintain the moisture of the tobacco," said Kassem. "We also recommend posting health warning signs for indoor smoking in hookah lounges, and encouraging bans of indoor hookah tobacco smoking in private homes."

The findings can be found published online in the journal Nicotine and Tobacco Research.