Selenium sulfide: what it treats, how to take it, side effects
Last updated September 3, 2026.
Selenium sulfide is an antifungal shampoo and lotion that treats dandruff, seborrheic dermatitis, and tinea versicolor. It slows the yeast that drives flaking and itching, and it comes in 1% over-the-counter and 2.5% prescription strengths.
What does it treat?
On the scalp it treats dandruff and seborrheic dermatitis, the greasy scale and itch around the scalp, eyebrows, and hairline. On the skin it treats tinea versicolor, the yeast infection that leaves lighter or darker patches on the chest and back. It manages the yeast; these conditions tend to recur, so periodic reuse is normal.
How do you take it?
As a shampoo: massage into the wet scalp, leave for 2 to 3 minutes, then rinse thoroughly. The usual schedule is twice a week for the first 2 weeks, then once a week for 2 to 4 weeks, then as needed for control. For tinea versicolor on the skin, the lotion is applied once daily for 7 days, lathered with a little water, left on for 10 minutes, then rinsed off completely. Rinsing is a safety step, not a nicety: rinse hair for at least 5 minutes to prevent discoloration, remove jewelry first, and never leave it on overnight. Keep it out of the eyes and off broken or inflamed skin.
Side effects to know
- Common: oily or dry hair and scalp, temporary hair loss, and hair discoloration, especially on dyed or permed hair when rinsing is skimped.
- Serious: significant skin irritation or an allergic reaction; stop and call your doctor if the skin becomes red, swollen, or blistered. Swallowing it is toxic, so keep it away from children.
Who should not take it?
Do not use it if you are hypersensitive to any ingredient, and do not apply it to broken or acutely inflamed skin, where it absorbs and stings. It is for external use only. Do not use it on children under 2 without a doctor's permission. If you are pregnant or breastfeeding, ask your doctor first. Rinse thoroughly every time, and wash your hands and under your nails after applying.
When is it an emergency?
Call 911 if someone swallows selenium sulfide, or for swelling of the face, lips, or throat or trouble breathing after use. Skin that blisters or peels after application needs prompt medical review. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
How often should I use selenium sulfide shampoo?
The standard schedule is twice a week for the first 2 weeks, then once a week for 2 to 4 weeks depending on response, then as needed to keep flakes down. Daily use is not the plan and usually irritates more than it helps.
Why did my hair change color after using it?
Selenium sulfide can discolor hair, especially hair that is dyed, bleached, or permed, when it is not rinsed out fully. The fix is in the directions: rinse for at least 5 minutes after the lather time, remove jewelry before washing, and wash hands and nails afterward.
Does selenium sulfide cause hair loss?
Temporary shedding is a listed side effect, usually modest and reversible. The flakes and inflammation of seborrheic dermatitis themselves loosen hairs too, so treating the scalp often improves the shedding that worried you in the first place. Persistent loss deserves a doctor's look.
Can I use it on my face?
With care. The 2.5% lotion is labeled for scalp and skin use like tinea versicolor, and clinicians do use it sparingly for facial seborrheic dermatitis, but it must stay out of the eyes and off broken skin, and it needs thorough rinsing. Ask before improvising around the eyes.
Is it the same as ketoconazole shampoo?
Different antifungal, same targets. Both treat dandruff, seborrheic dermatitis, and tinea versicolor, and people who plateau on one often respond to the other or to alternating them. Ketoconazole is prescription at 2% here too.
Do I need a prescription?
That depends on strength. The 1% shampoo is over the counter (Selsun Blue and generics), while the 2.5% lotion or shampoo is prescription. If the 1% version used correctly for a month has not controlled things, that is when the prescription strength or a second look makes sense.