Iodine is an essential mineral the thyroid needs to make its hormones, and it is also a powerful antiseptic. Those two uses are completely different: dietary iodine at microgram doses, and antiseptic iodine applied to skin. Confusing them is dangerous.
What is Iodine?
Iodine appears in the South African Medicine Price Registry in several unrelated forms:
| Form | Examples | Use |
|---|---|---|
| Povidone-iodine | Betadine solutions and douches (S2) | Antiseptic, applied to skin or mucous membranes |
| Iodinated contrast | Scanlux 300, Scanlux 370 (S4) | Injected for X-ray and CT imaging |
| Dietary iodine | Filibon and other multivitamins (S1) | Trace mineral in supplements |
| Trace element infusions | Addaven, Peditrace (S3) | Hospital intravenous nutrition |
These are not interchangeable in any sense. Antiseptic iodine is not for swallowing. Dietary iodine is measured in micrograms; antiseptic solutions contain thousands of times more.
Why the thyroid needs it. Thyroid hormones — T4 and T3 — are built around iodine atoms, and the thyroid is the only tissue that concentrates iodine for that purpose. Without enough, the gland cannot make enough hormone, and it enlarges trying to compensate — which is what a goitre is.
Iodine deficiency remains the world’s leading preventable cause of intellectual disability, because a developing brain depends on maternal thyroid hormone. In pregnancy, deficiency causes miscarriage, stillbirth and permanent impairment in the child.
South Africa has mandated iodised salt since 1995, and it worked — iodine deficiency and goitre fell substantially. That matters practically: if you are using non-iodised salt, sea salt or rock salt, or eating very little processed food, you may be getting less iodine than you assume.
What is Iodine commonly used for?
Dietary and thyroid:
- Preventing iodine deficiency and goitre.
- Supporting thyroid hormone production, which affects metabolism, temperature, heart rate, growth and brain development.
- Pregnancy and breastfeeding, where requirements rise substantially. Many pregnancy multivitamins include it for this reason.
- Radiation emergencies, where high-dose potassium iodide saturates the thyroid so it cannot take up radioactive iodine — a specific emergency use, not a general one.
- Preparing for thyroid surgery, or treating thyroid storm, under specialist care.
Antiseptic (povidone-iodine):
- Cleaning wounds, cuts and grazes.
- Skin preparation before surgery and before procedures.
- Pressure sores and infected ulcers.
- Mouthwashes and gargles, in some products.
- Vaginal preparations, in some products.
The most important thing about dietary iodine is that more is not better. Too little causes hypothyroidism and goitre. Too much also causes thyroid dysfunction — it can trigger both underactive and overactive thyroid, and in people with existing thyroid disease it can cause a marked flare.
High-dose iodine supplements, kelp, seaweed and iodine drops can cause real harm, and this is a common problem — these are marketed heavily for “thyroid support”, and are precisely the wrong thing for many people with thyroid conditions. Do not take high-dose iodine for a thyroid problem without your doctor’s direction. An underactive thyroid in South Africa is far more often autoimmune than iodine-deficient, and iodine does not treat it.
How Iodine fits into this medicine category
| Group | Examples | Role |
|---|---|---|
| Trace minerals | Iodine, selenium, zinc | Essential in microgram amounts |
| Thyroid hormone replacement | Levothyroxine | Treats hypothyroidism — the actual treatment |
| Antithyroid medicines | Carbimazole, propylthiouracil | Overactive thyroid |
| Antiseptics | Povidone-iodine, chlorhexidine | Skin disinfection |
| Diabetes medicines | Metformin, semaglutide (Ozempic) | Unrelated endocrine conditions |
An underactive thyroid is treated with levothyroxine, not iodine. See the endocrine and diabetes medicines hub.
What to check before using Iodine
Establish which iodine you mean. Antiseptic solutions are for skin. Dietary iodine is measured in micrograms.
For dietary iodine, speak to a doctor before supplementing if you:
- Have any thyroid condition — Hashimoto’s, Graves’ disease, nodules, or a previous thyroid operation. Iodine can destabilise all of them.
- Take levothyroxine, carbimazole or other thyroid medicine.
- Take lithium or amiodarone, both of which affect thyroid function.
- Are pregnant or breastfeeding. Requirements rise, but so does sensitivity — use a pregnancy multivitamin rather than a high-dose iodine product.
- Are considering kelp or seaweed supplements, where iodine content varies enormously between batches and can be extremely high.
- Have kidney disease.
For antiseptic povidone-iodine:
- Do not use it on large areas or for prolonged periods, particularly in newborns, pregnancy or thyroid disease — enough is absorbed to affect thyroid function.
- Do not use it if you are allergic to iodine.
- Avoid it on deep or puncture wounds without advice.
- Tell your doctor before a thyroid scan or radioactive iodine treatment, since recent iodine exposure interferes with both.
- Tell radiology staff about iodine or contrast reactions before any scan with contrast.
Possible cautions and when to ask a pharmacist or doctor
Dietary iodine at recommended amounts causes no problems. Excess causes a metallic taste, sore mouth and gums, increased salivation, stomach upset, and — most importantly — thyroid dysfunction in either direction.
Povidone-iodine commonly causes skin irritation and stains skin and fabric brown.
Get emergency help for:
- Swelling of the face, lips or tongue, difficulty breathing, or a widespread rash — iodine allergy is uncommon but real, and reactions to injected contrast can be severe.
- Swallowing antiseptic iodine, particularly by a child — take the bottle, and do not induce vomiting.
- Severe abdominal pain, vomiting or burns to the mouth and throat after ingestion.
Contact your doctor if you develop:
- Symptoms of an underactive thyroid — tiredness, weight gain, feeling cold, dry skin, constipation, low mood, slow pulse.
- Symptoms of an overactive thyroid — weight loss, palpitations, tremor, anxiety, heat intolerance, sweating, diarrhoea.
- A lump or swelling in the neck, difficulty swallowing, or a hoarse voice.
- A metallic taste or mouth soreness after taking an iodine supplement.
- Any thyroid symptom while taking kelp, seaweed or a high-dose iodine product — stop and get thyroid function checked.
Have thyroid function tested rather than self-supplementing. A blood test settles whether the thyroid is under- or overactive, and the treatments for those are opposite. Guessing wrong makes things worse.
Related medicine guides
Frequently asked questions
What is iodine used for? Two quite different things: as an essential dietary mineral the thyroid needs to make its hormones, and as povidone-iodine, an antiseptic applied to skin.
Can I take antiseptic iodine by mouth? No. Antiseptic solutions are for external use and are dangerous swallowed. Dietary iodine is measured in micrograms.
Will iodine fix my underactive thyroid? Almost certainly not. Underactive thyroid in South Africa is usually autoimmune, and it is treated with levothyroxine. High-dose iodine can make thyroid conditions worse.
Should I take a kelp or seaweed supplement? Not without medical advice. Iodine content varies enormously between batches and can be extremely high, which risks thyroid dysfunction.
Am I getting enough iodine? South Africa iodises table salt, which covers most people. If you use non-iodised, sea or rock salt and eat little processed food, you may be getting less than you assume.
Do I need more in pregnancy? Yes, requirements rise — but use a pregnancy multivitamin rather than a high-dose iodine product, and ask your doctor or midwife.
Why does povidone-iodine stain? The iodine itself is brown. It washes off skin over time and often permanently stains fabric.
Can too much iodine cause a thyroid problem? Yes — excess can cause both underactive and overactive thyroid, and can destabilise existing thyroid disease.