Vape clouds might seem innocent enough, especially if they are sweet-smelling and pleasant to inhale. However, that plume of fragrant fog is actually a complex array of chemical components, some of which are potentially harmful to human health.

Even if your e-liquid formulation is fairly simple, containing just a few mono-constituent chemical flavours, the resulting emissions profile might be quite different to what you’d expect. This is due to various chemical processes that occur during the vaporisation of the e‑liquid.

Some of these chemical processes involve intermolecular interactions of your e-liquid components and are generally quite unpredictable. The production of certain carbonyl compound emissions, however, is quite well understood.

Certain key carbonyls would, in fact, be expected to be present in the emissions profile of practically all conventional e-cigarette products. This is because they are common thermal degradation products of propylene glycol (PG) and vegetable glycerin (VG): the two main e-liquid constituents.

Taken from Sleiman et al. (2016). Emissions from electronic cigarettes: key parameters affecting the release of harmful chemicals. Environmental Science and Technology. July 2016.


Formaldehyde, acetaldehyde, acrolein and propanal are considered the key carbonyls that are expected to be present in PG/VG based e-cigarette emissions. The amounts present in vape will vary widely, dependent on several factors including the e-liquid composition and heated temperature (i.e. wattage) of the device.

Carbonyls form if you heat the e-liquid…but what is the human health significance of this phenomenon?

These low-molecular weight aldehydes are well-established harmful toxicants – especially when inhaled. For example, formaldehyde is considered to be carcinogenic to humans by several Expert and Authoritative Groups, including the International Agency for Research on Cancer (IARC), and these aldehydes have all been observed to cause damage to the respiratory tract of laboratory animals or humans.

In the UK, the MHRA has therefore stated that emissions data for (at least) formaldehyde, acetaldehyde and acrolein must be provided. However, these are not the only potentially harmful chemicals present in vape. It is also recommended that emissions data for other low molecular weight aldehydes, 2,3-diketones (e.g. diacetyl), certain volatile organic compounds (VOCs), tobacco-specific nitrosamines (TSNAs) and certain metal impurities (e.g. cadmium and lead) are also provided (where appropriate).

Further afield, the US FDA has identified a large number of “harmful and potentially harmful constituents” for which emissions data must be provided as part of a premarket tobacco product application (PMTA).

What to do with emissions data

Determining the levels of these key emissions from your e-cigarette product is a crucial step required of all devices and e-liquid combinations. Once they are identified, at what levels do these chemicals become a health concern to the typical vaper?

This is where a human health risk assessment comes in. Bibra has many years of experience conducting health risk assessments for a range of sectors and products (including e-cigarettes and medical devices). The process typically involves an in-depth evaluation of the available toxicological data and an assessment of any Expert Group hazard characterisation conclusions. Where the data is suitable, Bibra toxicologists are then able to propose a Tolerable Exposure level: a concentration considered to have no significant health concerns associated with it.

Such a Tolerable Exposure could be equated to an Analytical Evaluation Threshold (AET), for use in an analytical laboratory. If a detected emission is found to exceed the AET, then a health risk to the consumer cannot be ruled out with any confidence, and a more detailed health risk assessment may be required.

Ensuring consumer safety

One of the main goals of regulating e-cigarettes is to ensure the safety of the consumer (and also bystander). Such a goal may be achieved through banning/excluding (from use in e-liquids) certain substances known to be harmful to health; ensuring battery safety and/or enforcing manufacturers to show that the carbonyl emissions are below a certain level.

Human health risk assessment is a crucial step in confirming that use of your product does not give rise to any safety concerns.

A Bibra independent human health risk conclusion can go a long way in reassuring you, your clients and customers, and the regulators, that your product is safe for use. Get in touch to see how we can help.

Get in touch, we would be pleased to discuss how we can assist further.



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