Salicylate

What is it?

Salicylates are natural plant compounds — aspirin's chemical cousin — that plants make to defend themselves. Only plants make them, so meat, fish and dairy carry none at all. Berries, tomatoes, peppers, herbs and spices, mint, tea and almonds carry the most.

The reaction is not an IgE allergy. Baenkler (2008) describes it as a disturbance of arachidonic-acid and eicosanoid metabolism, set off by salicylates and by other COX inhibitors — which is why it appears as rhinitis, asthma and nasal polyps as often as anything digestive. That review carries the mechanism and no food: it names no quantity and no threshold.

How much a food contains

Malakar (2017) measured salicylic acid by GC-MS in 112 foods, per serve and per kilogram. An apple is 2.93 mg/kg peeled and 9.03 unpeeled, so taking the skin off removes about two thirds of it. The authors' own conclusion matters more than any single value: the size of the serving decides the dose more than the concentration does. Watercress, horseradish, hazelnut and walnut are not among those 112 foods.

Herbs and spices, the one group every study agrees on

Swain (1985) measured salicylic acid in 333 foods and put gherkins at 6 mg per 100 g, the highest of the vegetables; among the herbs and spices it names curry powder, paprika, thyme, garam masala and rosemary as very high. Paterson (2006) found salicylic acid in every spice it tested, up to 1.5 per cent by weight — fifteen thousand milligrams per kilo, where the highest single food Malakar measured reached 207 — and showed it is genuinely absorbed: blood and urine salicylate rose after a test meal. That figure is a ceiling for the group, not a value for one spice. Gajewska (2019) ranked culinary herbs and spices and placed dried basil and cumin highest, then dried oregano and cloves; it publishes the order and no concentration, and it measures the dried herb rather than the fresh leaf.

The tables disagree, and the gap is the useful part

Scotter (2007) measured 76 foods by GC-MS and found detectable salicylic acid in only 37 of them, the highest being dried herbs at 28.6 mg/kg, and states plainly that its results show many inconsistencies with earlier data. Venema (1996) put free-plus-bound salicylic acid at 0 to 1 mg/kg in vegetables and fruit against 3 to 28 in herbs and spices — and Malakar's unpeeled apple, at 9.03, is three to nine times that ceiling for fruit. Neither measurement cancels the other, and both report ranges by group rather than a value for each food. What all of them agree on is that herbs and spices are the high group.

Why two honest tables can differ

In the plant these acids sit mostly bound — hydroxybenzoic acids as glucosides, hydroxycinnamic acids as esters — which Herrmann (1989) describes for the phenolic acids as a family. A method that measures free acid and a method that hydrolyses first therefore return different numbers for the same food. Herrmann publishes no salicylate figure of its own; what it settles is the chemistry.

What a day actually delivers

Janssen (1996) gave six volunteers pure aspirin or salicylic acid and recovered 77 to 80 per cent in the urine within 24 hours, which makes urine a usable measure of intake. Seventeen volunteers from fourteen countries, eating whatever they normally eat, excreted a median of 1.4 mg in 24 hours, and the figure rose with the fibre in the diet, which points at vegetables as the main carrier. Wood (2011) turns this into shares: in a Scottish population taking 4.42 mg a day for men and 3.16 for women, alcoholic drinks supplied 22 per cent of it, herbs and spices 17, fruit 16, juices and other soft drinks 13, tomato-based sauces 12 and vegetables 9. Those shares belong to that diet. Both measure intake and not tolerance: neither asks what dose provokes a symptom.

Aspirin itself is not in food

Venema (1996) searched 30 foods reputed high in salicylates, down to 0.02 mg/kg in fresh produce and 0.2 in dried, and found no acetylsalicylic acid in any of them. Of Scotter's 76 samples exactly one contained it — a curry sauce, at 0.34 mg/kg. A salicylate-rich meal is not a dose of aspirin.

How uncertain all of this is

Duthie (2011) reports that published estimates of daily salicylic acid intake range from 0.4 to 200 mg, a five-hundredfold spread across the literature, and names tomato-based sauces, fruit and fruit juice, tea, wine, herbs and spices as the major UK sources. The intakes measured above sit at the bottom of that range. Read each level on this axis as an ordering of foods rather than as a dose.

Where the additives come in

Many additives carry a level here for one reason only: an elimination diet excludes them, and the EAACI urticaria guideline itself rates that diet as low-evidence and unproven. Silva (2022) reports allergic, behavioural and neurocognitive effects for synthetic colours as a class and names no individual colour, so it ranks the family and cannot value any member of it. Six colours — tartrazine, quinoline yellow, sunset yellow, carmoisine, ponceau 4R and allura red — are named in Annex V of the additives regulation and must carry the children's attention warning on the label; that is a different endpoint from this axis, attention rather than salicylate.

Source: Baenkler H-W., Dtsch Arztebl Int 105:8 (2008) 137-142, for the mechanism and the clinical spectrum; Malakar S., Gibson P.R., Barrett J.S. & Muir J.G., J Food Compos Anal 57 (2017) 31-39, salicylic acid by GC-MS in 112 foods, per serve and per kilogram; Swain A.R., Dutton S.P. & Truswell A.S., J Am Diet Assoc 85 (1985) 950-960, salicylic acid in 333 foods, for the gherkin figure and the herbs and spices it names; Paterson J.R. et al., J Agric Food Chem 54 (2006) 2891-2896, for the spice ceiling and its absorption; Gajewska D., Kęszycka P.K. & Szkop M., Food Funct 10 (2019) 7037-7041, for the order of the culinary herbs; Scotter M.J. et al., Food Chem 105 (2007) 273-279, for the 37 of 76 and the dried-herb maximum; Venema D. et al., J Agric Food Chem 44 (1996) 1762-1767, for the group ranges and the absence of acetylsalicylic acid; Herrmann K., Crit Rev Food Sci Nutr 28:4 (1989) 315-347, for the bound forms these acids take in plants; Janssen P.L. et al., Am J Clin Nutr 64 (1996) 743-747, for the measured urinary excretion; Wood A. et al., Mol Nutr Food Res 55 Suppl. 1 (2011) S7-S14, for the intake and the share each food group contributes; Duthie G.G. & Wood A.D., Food Funct 2 (2011) 515-520, for the range of published intakes; Silva M.M. et al., Foods 11:3 (2022) 379, for the standing of synthetic colours as a class; Regulation (EC) No 1333/2008, Article 24 and Annex V, for the six colours that require the children's attention warning

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