Spinach is not a meaningful source of iodine, and iodine does not clog pores

An Instagram Reel caption from the account skinbyblair tells people with acne to look at their salad:

Spinach is also high in iodine, and for some people, too much iodine can overstimulate your oil glands. This can lead to clogged pores and acne, especially if you're prone to breakouts or suddenly increase your intake. So if you've been loading up on spinach lately and noticing more blemishes, this could be why!

Two notes on what is being assessed. Instagram cannot be archived by the Wayback Machine — both an automated snapshot and a manual request failed — so the caption above is the text as supplied at intake. The video itself was not viewed, and nothing here is a characterisation of what is said in it. If the audio makes different claims, they are outside this piece.

The caption makes three separate assertions, and they fail in three different ways. One is largely right, one is contradicted by direct measurement, and one takes a real dermatological phenomenon and re-points it at the wrong dose, the wrong mechanism and the wrong disease.

What the caption gets right

Spinach is a strong source of vitamin A, and the piece deserves credit for it. The NIH Office of Dietary Supplements vitamin A fact sheet lists half a cup of boiled frozen spinach at 573 mcg RAE, 64% of the Daily Value — second only to baked sweet potato on its food table. That figure is already adjusted for the fact that plants supply provitamin A carotenoids rather than retinol: one mcg RAE equals "1 mcg retinol, 2 mcg supplemental beta-carotene, 12 mcg dietary beta-carotene." ODS notes the body absorbs "up to 75% to 100% of retinol and, in most cases, 10% to 30% of beta-carotene from foods," and that "cooking and heat treatment can increase the bioavailability of beta-carotene."

The iron claim is correct with a caveat. Per the ODS iron fact sheet, "plants and iron-fortified foods contain nonheme iron only," and "heme iron has better bioavailability than nonheme iron." How much spinach iron you actually absorb depends on what you eat with it — ODS names ascorbic acid and phytate as the modifiers. That is a real caveat, not a rebuttal.

The vitamin C claim was not assessed. No source consulted for this piece gives spinach's vitamin C content, so we take no position on it.

"Spinach is high in iodine" is false

This is the load-bearing sentence, and it is the one the measurement data contradict.

The USDA, FDA and ODS-NIH Database for the Iodine Content of Common Foods gives the numbers directly:

For scale, from the same table: baked cod, 3 oz, 146 mcg. Nori, 2 tbsp flaked, 116 mcg. A quarter-teaspoon of iodized salt, 78 mcg. A cup of whole milk, 82 mcg. One hard-boiled egg, 31 mcg. Three cups of raw spinach contain about a fifth of the iodine in a single egg, and about a fourteenth of what is in a cup of milk.

These are pooled analytical samples with small counts — 27 for raw, 8 for boiled — and the spread on raw spinach is wide, which fits what the ODS iodine fact sheet says about soil: "Most fruits and vegetables are poor sources of iodine, and the amounts they contain are affected by the iodine content of the soil, fertilizer use, and irrigation practices." Spinach does not appear in that fact sheet's food table at all. Even the single highest raw-spinach sample in the database, 36 mcg per 90 g, is under half a cup of milk.

Some arithmetic, shown rather than asserted — this is our calculation from the USDA and ODS figures, not a number either source publishes. The adult iodine RDA is 150 mcg/day and the Tolerable Upper Intake Level for adults is 1,100 mcg/day. At 6.0 mcg per 90 g, hitting the RDA takes roughly 2.25 kg of raw spinach; reaching the UL takes about 16.5 kg, on the order of 550 cups a day. Use the highest sample ever recorded instead of the mean and the UL still needs about 2.75 kg, roughly 90 cups. Three cups supply 4% of the RDA. ODS puts it plainly: "In most people, iodine intakes from foods and supplements are unlikely to exceed the UL."

One thing we did not use: several consumer pages quote tidy per-100 g iodine figures for spinach that sit close to the USDA values. They carry no attribution, so we dropped them, even though they would have supported the same conclusion.

Iodine and skin: real, but not this

Iodine does cause skin reactions. Saying otherwise would be wrong, and the caption is not inventing the phenomenon from nothing.

Dermatologist F. William Danby, writing in the Journal of the American Academy of Dermatology in 2007, concedes it directly: "Kelp is recognized as causing an acneiform eruption where the iodide source is indeed high, and there is little doubt that a papular and papulopustular acneiform eruption can be triggered by halides." DermNet NZ's page on halogenodermas lists the causes: iodine antiseptics on broken skin, potassium iodide, expectorants, multivitamins and tonics, amiodarone, radiocontrast media, and — the only dietary entry — "high-iodine containing foods such as seaweed, seafood and iodised salt, with rare cases of iododerma reported following prolonged and excessive ingestion." No vegetable appears. DermNet also notes it generally takes months of continuous exposure.

What that looks like in practice is documented in a 2022 case report — a single case, the weakest design cited here, and worth labelling as such. A 40-year-old man took muscle-building supplements containing iodide and bromide for four months, then developed crusted papules and nodules on his face, neck and trunk with low-grade fever. Biopsy showed intraepidermal abscesses and dense neutrophil infiltrates; the authors propose a type 2 delayed hypersensitivity reaction. It cleared after he stopped the supplements. No dose threshold is given. It bears no resemblance to a few extra blemishes after eating salad.

The caption's mechanism is also inverted. DermNet's proposed pathway is that "excretion of halogen via sweat or oil glands may result in an inflammatory reaction in the skin." The oil gland is the exit route, and the outcome is inflammation. Nothing in these sources says iodine makes the gland produce more sebum, which is what "overstimulate your oil glands" means.

And the disease is different. Danby's central distinction is exactly the one the caption collapses: "but the hallmark of acne, the comedo, is not part of the initial lesion in this picture. Comedones may appear as secondary lesions." His conclusion: "To summarize, there is no evidence to support iodides as a cause of comedonal acne." The clogged pore the caption names is the thing the literature says iodide does not produce.

Where our own case is weak

Danby's piece is a letter, not a study, and he says so about the gap: "The definitive work needed to answer the question would be a blinded trial of a very high iodide diet in a teenaged or young twenties population. I suspect it would be a significant challenge to obtain ethics approval, let alone volunteers, for such a study." There is no trial disproving dietary iodine as an acne cause. His own dose illustration gives the scale: matching a 750 mg/day therapeutic dose of potassium iodide would take 1,140 litres of milk a day.

The 2024 American Academy of Dermatology acne guidelines — a GRADE systematic review — do not help either way. Their diet question covers low-glycemic-load, low-dairy, low-whey, omega-3 and chocolate. Iodine is not among the exposures evaluated at all. That is an absence of consideration, not a clearance. On what they did assess: "Available evidence is conflicting on low-glycemic-load diet for acne treatment," and "Available evidence is insufficient to develop a recommendation on the use of low dairy diet, low whey diet, omega-3 fatty acids, and chocolate on acne treatment." Four low-glycemic-load trials are listed, three favourable and one null, and the guideline names dietary interventions for acne as an explicit evidence gap.

There is also a 1961 Archives of Dermatology paper, Hitch and Greenburg's "Adolescent acne and dietary iodine," which both sides of this argument lean on. We could not read it — only the PubMed record, which carries no abstract. Confident conclusions are circulated from it at second hand; we could not verify them, so none of them appear above.

Why E and not D

D is for a claim that is not technically false but framed to mislead — a real finding pushed past what it shows. That grade is tempting here, because the halide literature is genuinely real and the vitamin A claim is genuinely right. But the sentence that carries the argument is not a stretched finding. "Spinach is also high in iodine" is contradicted by direct measurement, and once it goes, nothing links iododerma to a bowl of leaves.

Not C either. C is for genuinely split evidence, and there is no split on spinach's iodine content — it is measured, and it is low. Whether diet affects acne at all is a live question, as the AAD guideline shows. That is a different question, and this claim does not get to borrow its uncertainty.

Eat the spinach. If your skin is changing, this is not the reason — and what to do about acne is a question for a clinician, not for this piece.