Slush ice drinks with glycerol: refreshments with potential undesired health effects

Glycerol (also known as glycerine or glycerin) is a sweet-tasting, colourless liquid that is chemically classified as an alcohol and freezes at 18 degrees Celsius (°Cshort fordegrees Celsius). Both vegetable and animal fats and oils contain glycerol. It is an intermediate product produced during the alcoholic fermentation of sugar-containing solutions, which is why wine, for instance, also contains small amounts of glycerol.

In the EU, glycerol is authorised as food additive E 422 for use in foods, including flavoured drinks. No maximum level has been defined and it is possible to use as much glycerol as necessary.

Glycerol is not only used in food, but also for therapeutic purposes, for example to reduce elevated intracranial pressure. Studies have shown that the lowest effective dose is 250 milligrams (mgshort formilligram) of glycerol per kilogram (kgshort forkilogram) of body weight. The BfRshort forGerman Federal Institute for Risk Assessment has used this dose as a reference in its assessment of the potential health risks associated with the consumption of slushies.

The glycerol levels were measured in a total of 62 slushy samples and submitted to the BfRshort forGerman Federal Institute for Risk Assessment. The evaluation of the measured concentrations of glycerol revealed that even when consuming a slushy of less than 200 mL, younger children may already be ingesting amounts of glycerol that correspond to or even exceed the therapeutically effective dose. For example, a 5-year-old child with a body weight of 20 kgshort forkilogram would ingest this amount when consuming a slushy of just under 200 mL with the average measured glycerol concentration (26.24 grams (g) per litre (L)).

The highest measured value of 142 g/L was found in a ‘beverage syrup’, which is a ready-to-drink beverage. A glycerol concentration of more than 25 g/L was found in just under half of the samples (approx. 48 %). In eight samples (approx. 13 %), the measured value was less than 1 g/L. Glycerol could not be detected in about a third of the samples (approx. 32 %).

No general statement can be made about the probability of health consequences, as this depends on the glycerol concentration in the respective slushy, the amount consumed and the body weight of the consumer. 

However, in the view of the BfRshort forGerman Federal Institute for Risk Assessment there are health concerns if the consumption of a slushy results in a glycerol intake that corresponds to or exceeds the therapeutically (for the purpose of reducing increased intracranial pressure) effective dose of 250 mgshort formilligram/kgshort forkilogram body weight. According to scientific studies on the efficacyClose dialogefficacyPositive Predictive ValueTo glossary and metabolization of glycerol, undesirable side effects have been recorded, including headaches, nausea, vomiting, diarrhoea and light-headedness.

When conducting a health risk assessment of glycerol in slushies, special attention needs to be paid to children. When children consume a slushy that contains glycerol they are exposed to a higher dose (in mgshort formilligram of glycerol per kgshort forkilogram body weight) than adults due to their lower body weight. Accordingly, the volume of a slushy required to result in a therapeutically effective dose of 250 mgshort formilligram/kgshort forkilogram body weight is smaller for children than for adults.

It has been calculated that a child aged around 5 years with a body weight of 20 kgshort forkilogram that consumes a slushy of just under 200 mL with the mean of the measured glycerol concentrations of around 26 g/L ingests enough glycerol to constitute a therapeutically effective dose.

There is in general very little data on the toxicity of glycerol after oral ingestion by children. It is also not possible to reliably assess whether glycerol leads to a reduction in intracranial pressure in healthy children to the same extent as in children with increased intracranial pressure, as the BfRshort forGerman Federal Institute for Risk Assessment does not have corresponding data. However, the BfRshort forGerman Federal Institute for Risk Assessment does assume this in the sense of a conservative approach and considering the chemico-physical (osmotic) properties of glycerol.

Reduced intracranial pressure can cause several symptoms, for example headache, nausea, vomiting, dizziness, cranial nerve paralysis, double vision (diplopia) and impaired hearing.

In response to the BfRshort forGerman Federal Institute for Risk Assessment's enquiries to the German poison centres in 2024, one case was reported in which the symptoms of an eight-year-old child (nausea, diarrhoea, fever) were possibly linked to the effects of glycerol in a slushy. Internationally, two cases were initially reported in 2021 and 2022 in which children were hospitalised after consuming slushies. Furthermore, a publication by Brothwell et al.short foret alii (lat. "and others") (2025) described 21 cases of children who presented with symptoms after consuming slushies in the UK and Ireland between 2009 and 2024. It is not certain that the symptoms described in these case reports are due to glycerol in slushies. However, the BfRshort forGerman Federal Institute for Risk Assessment is of the opinion that the possibility should be taken into account. 

A general problem in detecting possible cases is that symptoms such as nausea, diarrhoea and headache may not be associated with the consumption of slushies. This could lead to an underestimation of the health risk.

A value for an acceptable daily intake (ADIshort forAcceptable Daily Intake) at which health impairments are not to be expected has not been set for the food additive glycerol (E 422). The European Food Safety Authority (EFSAshort forEuropean Food Safety Authority) assessed the use of glycerol as a food additive in 2017 and concluded that there was no need to derive an ADIshort forAcceptable Daily Intake and that, according to available data (including data on use levels), there were no health concerns for the general population. Measured values that showed high concentrations of glycerol in slushies, as have now been determined, were not available to EFSAshort forEuropean Food Safety Authority at that time.

To avoid any undesirable health effects from glycerol intake, consumers can avoid drinking slushies.

Manufacturers of slushies could check whether the use of glycerol is required (about one third of the measured samples did not contain glycerol) or whether the glycerol concentration could at least be reduced (in the samples containing glycerol, concentrations were in a relatively wide range of less than 1 g/L to 142 g/L).