PEG / macrogol
Where? Laxatives, tablets, injections and cosmetics.
Immediate allergy, sometimes severe.
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Medicines & perioperative care
Excipients, colourings and additives
Medicines and foods: identify the real cause without avoiding everything
A medicine contains more than its active ingredient. It also contains excipients used to stabilise, preserve, thicken, colour or make the product easier to administer. Most are very well tolerated, but hypersensitivity to some excipients is now well documented.
In this sheet
The most important message
Reacting to a medicine does not necessarily mean allergy to its active ingredient. If you have reacted to several unrelated medicines, or only to certain brands or formulations, an excipient may sometimes be responsible.
Four essential points
Excipient allergies are rare, but real
They may explain repeated reactions to medicines with very different active ingredients.
The exact formulation matters
Two medicines with the same active ingredient may contain different excipients.
‘Excipients’ does not mean ‘all excipients’
Allergy to one particular excipient does not justify arbitrarily avoiding every additive.
Diagnosis must identify the precise cause
Brand name, dosage form, manufacturer and complete ingredient list are often essential.
When should an excipient be considered?
Excipient hypersensitivity may be considered when someone reacts to several medicines whose active ingredients are chemically unrelated, tolerates some formulations but not others, or reacts after certain injections or biological medicines.
- reactions to several medicines without an obvious chemical relationship;
- reaction to one brand or form but tolerance of another containing the same active ingredient;
- unexplained reactions to certain laxatives, depot injections or biological medicines;
- repetition of the same type of reaction with products sharing an excipient.
Which excipients are genuinely recognised in allergology?
There is no single ‘allergenic excipient’. Some substances are better documented than others, but their significance depends on the clinical context and formulation.
Polysorbates
Where? Injections, vaccines, biological medicines and cosmetics.
Structurally related to PEG; specialist assessment.
Poloxamers
Where? Some pharmaceutical formulations.
Reactions reported, sometimes related to PEG.
Gelatin
Where? Capsules, vaccines, solutions or medical products.
IgE reactions are possible.
CMC / carmellose
Where? Injections, tablets, eye drops and suspensions.
Documented anaphylaxis.
Povidone
Where? Tablets, antiseptics and injections.
Immediate reactions are possible.
Mannitol
Where? Tablets, inhaled products and some infusions.
Rare but documented.
Metabisulphites
Where? Some injections, adrenaline and anaesthetics.
Mainly non-IgE hypersensitivity; see the dedicated sulphites sheet.
Other substances
Where? Parabens, benzyl alcohol, EDTA and metacresol depending on the formulation.
Much rarer causes.
| Excipient | Where might it be found? | Key point |
|---|---|---|
| PEG / macrogol | Laxatives, tablets, injections and cosmetics. | Immediate allergy, sometimes severe. |
| Polysorbates | Injections, vaccines, biological medicines and cosmetics. | Structurally related to PEG; specialist assessment. |
| Poloxamers | Some pharmaceutical formulations. | Reactions reported, sometimes related to PEG. |
| Gelatin | Capsules, vaccines, solutions or medical products. | IgE reactions are possible. |
| CMC / carmellose | Injections, tablets, eye drops and suspensions. | Documented anaphylaxis. |
| Povidone | Tablets, antiseptics and injections. | Immediate reactions are possible. |
| Mannitol | Tablets, inhaled products and some infusions. | Rare but documented. |
| Metabisulphites | Some injections, adrenaline and anaesthetics. | Mainly non-IgE hypersensitivity; see the dedicated sulphites sheet. |
| Other substances | Parabens, benzyl alcohol, EDTA and metacresol depending on the formulation. | Much rarer causes. |
What about lactose in medicines?
Lactose is not milk protein. Lactose is a sugar, and lactose intolerance is not an allergy. In people with severe milk protein allergy, rare problems have nevertheless been reported with some pharmaceutical preparations containing lactose contaminated by traces of protein. This does not justify automatically prohibiting every lactose-containing tablet.
Food colourings: annatto, carmine and what we really know
Genuine allergies to food colourings occur, but remain rare. They are best documented with certain natural colourings.
Annatto – E160b
Annatto is extracted from Bixa orellana seeds. It is used to colour some cheeses, fats, desserts, snacks and processed foods yellow-orange. Hives, angioedema and anaphylaxis have been reported, but remain exceptional.
Carmine / cochineal – E120
Carmine comes from cochineal insects. It may be found in red or pink foods, drinks, sweets, cosmetics and some coloured medicines. IgE-mediated allergy and anaphylaxis are clearly documented.
One particularly instructive example is someone who reacted to a generic formulation of a coloured medicine containing carmine while tolerating another formulation of the same active ingredient without carmine.
Tartrazine – E102
Tartrazine is a synthetic yellow colouring. Hives or bronchospasm have been reported, but confirmed reactions are much less common than generally believed. Evidence does not support routinely avoiding every azo dye in every patient with asthma.
Other colourings
Saffron, paprika, curcumin, Patent Blue V or indigotine may be considered depending on the context, but the presence of a colouring alone is not enough to explain a reaction.
How is the diagnosis made?
Reconstruct exactly what was taken
If possible, bring the brand name, strength, form (tablet, capsule, syrup, injection, etc.), manufacturer, box, leaflet, a photograph of the ingredient list and batch number if available.
Compare formulations
A reaction to brand A with tolerance of brand B containing the same active ingredient may prompt a search for excipients found only in the first formulation.
Skin tests
There is no universal ‘excipient allergy’ panel. Depending on the excipient and context, a specialist team may offer skin prick tests, intradermal testing, tests with pure excipient or a formulation, and sometimes in-vitro tests.
Food colourings. For most food additives, skin tests have little diagnostic value. Exceptions exist when genuine IgE allergy to a natural colouring is suspected, particularly carmine or cochineal.
Challenge test
When needed, a controlled challenge may compare a medicine containing the excipient with an alternative formulation, or confirm a reaction to a food additive.
What should I bring to the consultation?
- Box / blister pack / bottle
- Identifies the exact formulation.
- Leaflet or photograph of excipients
- Helps compare tolerated products with those that caused a reaction.
- Manufacturer name
- Excipients may vary by manufacturer.
- Batch number
- Useful in some investigations or pharmacovigilance reports.
- List of previously tolerated medicines
- Helps identify shared excipients or, conversely, excipients that are absent.
| Item | Why it is useful |
|---|---|
| Box / blister pack / bottle | Identifies the exact formulation. |
| Leaflet or photograph of excipients | Helps compare tolerated products with those that caused a reaction. |
| Manufacturer name | Excipients may vary by manufacturer. |
| Batch number | Useful in some investigations or pharmacovigilance reports. |
| List of previously tolerated medicines | Helps identify shared excipients or, conversely, excipients that are absent. |
What really needs to be avoided?
The aim is precise avoidance, not an endless list. Overly broad avoidance may unnecessarily complicate treatment or diet.
- Clearly identified excipient
- Avoid that excipient and check relevant formulations.
- Confirmed natural colouring
- Look for its name and/or E number in the relevant foods, medicines or cosmetics.
- Cause only suspected
- Do not broaden avoidance before investigation.
- Essential medicine
- Find an alternative formulation with the doctor, pharmacist or allergist.
- Reactions to several medicines
- Systematically compare shared excipients.
| Situation | Action |
|---|---|
| Clearly identified excipient | Avoid that excipient and check relevant formulations. |
| Confirmed natural colouring | Look for its name and/or E number in the relevant foods, medicines or cosmetics. |
| Cause only suspected | Do not broaden avoidance before investigation. |
| Essential medicine | Find an alternative formulation with the doctor, pharmacist or allergist. |
| Reactions to several medicines | Systematically compare shared excipients. |
Common myths
- ‘A medicine allergy always concerns the active ingredient.’
- False.
- ‘All excipients are inert.’
- No, but allergies remain rare.
- ‘PEG equals polysorbate, so everything is forbidden.’
- No. Assessment must be individualised.
- ‘Natural means non-allergenic.’
- False: carmine and annatto may cause genuine allergies.
- ‘All food colourings are dangerous.’
- False.
- ‘Tartrazine always causes allergy in people with asthma.’
- No.
- ‘If I reacted to a generic, I am allergic to the whole active ingredient.’
- Not necessarily.
- ‘Lactose in a tablet means milk protein.’
- No.
| Myth | SOS Allergo message |
|---|---|
| ‘A medicine allergy always concerns the active ingredient.’ | False. |
| ‘All excipients are inert.’ | No, but allergies remain rare. |
| ‘PEG equals polysorbate, so everything is forbidden.’ | No. Assessment must be individualised. |
| ‘Natural means non-allergenic.’ | False: carmine and annatto may cause genuine allergies. |
| ‘All food colourings are dangerous.’ | False. |
| ‘Tartrazine always causes allergy in people with asthma.’ | No. |
| ‘If I reacted to a generic, I am allergic to the whole active ingredient.’ | Not necessarily. |
| ‘Lactose in a tablet means milk protein.’ | No. |
Key points
- Excipient allergy is rare but may explain reactions to several unrelated medicines.
- The brand name and exact formulation are essential.
- PEG or macrogol, polysorbates, gelatin, CMC, povidone and mannitol are among the best-documented excipients.
- Genuine food-colouring allergies are rare; carmine E120 and annatto E160b are among the best described.
- A synthetic colouring such as tartrazine causes genuine allergy much less often than generally believed.
- The aim is to identify the precise cause and avoid unnecessary restrictions.
Download the validated sheet
Find these points in the validated patient document (available in French).
You may also want to read
Main references
- Garvey LH, et al. Hypersensitivity to Excipients in Drugs: An EAACI Position Paper. Allergy. 2026.
- Stone CA Jr, et al. Anaphylaxis to Excipients in Current Clinical Practice: Evaluation and Management.
- Seth et al. Excipient induced allergies in oral medications: unravelling the covert threat - a systematic review. Internal Medicine Journal. 2025.
- Babbel J, et al. Adverse reactions to food additives. J Food Allergy.
- AAAAI. Allergic to the Fine Print: Food Allergy to Additives, Rare but Real.
- Greenhawt et al. / natural color additives literature: annatto and carmine.
- Takeo et al. Review of cochineal / carmine allergy.
Information for patients and carers. This sheet does not replace medical consultation or personalised advice from your healthcare professional.
Scientific review: September 2026 · sosallergo.fr