Adding a touch of cinnamon or vanilla to your e-cigarette might ease your stress levels, but the same can't be said for your white blood cells.

That's the take-home message from a study conducted by a team of US researchers who examined the impact vaporised flavour additives had on our health. It turns out they aren't as innocent as we'd thought.

Naturally occurring chemicals such as cinnamaldehyde, acetoin, ortho-vanillin, and maltol are what give cinnamon, butter, vanilla, and caramel their characteristic flavours.

We've happily swallowed them in our food for generations with no evidence of ill effects, so few have questioned whether inhaling the same compounds as a vapour might be a cause for concern.

Yet suspected links between flavouring chemicals such as diacetyl and respiratory conditions such as bronchitis have hinted at a potential for serious health problems.

To gain a better understanding of what was going on, scientists from the University of Rochester Medical Centre in the United States exposed white blood cells called monocytes to seven common e-cigarette flavourings, and looked for signs of oxidative stress.

The results showed there's a clear need to have a rethink on just how safe flavoured e-cigarettes might be.

The researchers found flavourings produced compounds called reactive oxygen species – substances that are known to damage cell structures in high enough concentrations.

White cells exposed to the flavourings also pumped out a signalling protein called interleukin 8 in concentrations that went up in accordance with the dose.

This protein acts as a chemical siren for other immune cells, calling them to a site of infection or cellular damage. In other words, the cells were responding to the presence of flavourings as if they recognised them as hazardous.

Lastly, they looked at the general health or viability of the cells as they were exposed to different additives, to get some idea of the flavourings' general toxicity.

Some of the additives were more toxic than others, but it was in combination that they really did some damage.

"Cinnamon, vanilla, and butter flavouring chemicals were the most toxic but our research showed that mixing flavours of e-liquids caused by far the most toxicity to white blood cells," says toxicologist Thivanka Muthumalage.

Putting the results into perspective, there's a big leap between white blood cells screaming for help in a petri dish and a physiological reaction in an otherwise healthy human being.

But it does add a new level of complexity to the debate over how we might want to deal with the growing fad of swapping old fashioned cigarettes for vaping.

"Currently, these are not regulated, and alluring flavour names, such as candy, cake, cinnamon roll and mystery mix, attract young vapers," says the study's senior author, Irfan Rahman.

"Our scientific findings show that e-liquid flavours can, and should, be regulated and that e-juice bottles must have a descriptive listing of all ingredients. We urge regulatory agencies to act to protect public health."

A couple of years ago, the US Food and Drug Administration (FDA) announced it would use the same set of rules to regulate both electronic and non-electronic cigarettes.

This was overturned last year, when the FDA released a new set of regulations, focussing on beating nicotine addiction by relaxing laws surrounding the vaporising of tobacco compounds.

Whether this kind of research impacts on future changes to regulations is anybody's guess. More research will no doubt fill in the missing details on exactly how vaping in all its forms affects our bodies.

In the meantime, if e-cigarettes are your way to beat an addiction, you might want to consider how badly you want that cinnamon puff. 

This research was published in Frontiers in Physiology.