Citric acid occurs naturally in the body, is 'generally recognized
as safe' in the USA, and is used in pharmaceutical inhalation products.
However, thermal degradation of citric acid can occur at the operating
temperatures of some vaping devices. Starting at around 175-203°C,
citric acid can degrade to form citraconic anhydride and its isomer
These anhydrides are respiratory sensitizers - chemicals that, on
inhalation, can trigger an allergic reaction varying from hay fever
symptoms to anaphylactic shock.
‘Citric acid in an e-liquid may lead to significant amounts of citraconic and/or itaconic anhydride in vapor that can trigger an allergic reaction.’
Scientists at British American Tobacco used gas chromatography
coupled to time-of-flight mass spectrometry to analyze the vapor
generated when an e-liquid containing citric acid is heated in a vaping
device. The device used was a first-generation (cig-a-like)
e-cigarette. The scientists were able to measure significant amounts of
anhydrides in the vapor.
The results are presented today the annual conference of the Society for Research on Nicotine and Tobacco in Florence, Italy.
'Citric acid in an e-liquid may lead to significant amounts of
citraconic and/or itaconic anhydride in vapor, depending on the
device,' says Dr Sandra Costigan, Principal Toxicologist Vaping
'But we believe that flavorings can be used responsibly and we have
already rejected the use of some flavorings in our products. Based on
this case study using a first generation e-cigarette, we recommend that
the potential for formation of citraconic and itaconic anhydrides should
be investigated further before commercialization of e-liquids
containing citric acid,' Costigan said.
Many in the public health community believe e-cigarettes offer
great potential for reducing the public health impact of smoking.
Public Health England, an executive body of the UK Department of Health,
recently published a report saying that the current expert estimate is
that using e-cigarettes is around 95% safer than smoking cigarettes.
The Royal College of Physicians have said that the public can be
reassured that e-cigarettes are much safer than smoking and that they
should be widely promoted as an alternative to cigarettes.