Selenium sulfide and pyrithione zinc are medicated anti-dandruff ingredients that work through different mechanisms to treat scalp conditions. Selenium sulfide remains a licensed pharmacy medicine in the UK, available as a 2.5% shampoo formulation for dandruff and seborrhoeic dermatitis. However, pyrithione zinc has been prohibited in UK and EU cosmetic products since 2022 and is not licensed as a medicine by the MHRA, making its availability extremely limited. Understanding the differences between these treatments, their regulatory status, and evidence-based alternatives helps patients and healthcare professionals make informed decisions about managing scalp conditions effectively and safely.

What Are Selenium Sulfide and Pyrithione Zinc?

Selenium sulfide and pyrithione zinc are active ingredients used in medicated products to treat dandruff, seborrhoeic dermatitis, and other scalp conditions. These agents work through different mechanisms but share the common goal of reducing scalp flaking, itching, and inflammation.

Selenium sulfide is an antifungal and cytostatic agent available in the UK as a 2.5% formulation, which is classified as a Pharmacy (P) medicine. It works by reducing the turnover rate of epithelial cells on the scalp, thereby decreasing the excessive shedding that characterises dandruff. Additionally, selenium sulfide possesses antifungal properties against Malassezia species, yeasts that colonise the scalp and contribute to seborrhoeic dermatitis. The compound also has mild antibacterial effects. In the UK, it is available as Selsun shampoo.

Pyrithione zinc (also known as zinc pyrithione) is an antimicrobial and antifungal agent that has historically been used in anti-dandruff products. Its mechanism of action involves disrupting fungal cell membrane transport and inhibiting the growth of Malassezia yeasts. However, it's important to note that since 2022, zinc pyrithione has been prohibited in cosmetic products in the UK and EU due to regulatory changes. It is not licensed as a medicine by the Medicines and Healthcare products Regulatory Agency (MHRA), and its availability in the UK is now very limited.

Other licensed treatments for dandruff and seborrhoeic dermatitis in the UK include ketoconazole 2% shampoo, which is often recommended as a first-line treatment alongside selenium sulfide. These medicated shampoos have established safety profiles when used as directed and represent evidence-based options for managing scalp conditions.

Comparing Effectiveness for Dandruff and Scalp Conditions

Clinical evidence suggests that both selenium sulfide and antifungal treatments are effective for dandruff and seborrhoeic dermatitis, though their efficacy profiles differ.

For dandruff (pityriasis capitis), selenium sulfide has demonstrated good efficacy in reducing visible flaking. Studies suggest that regular use of selenium sulfide can lead to significant improvement in scalp flaking after several weeks of use. Historically, pyrithione zinc has also shown effectiveness in clinical studies, though direct comparative data between the two agents is limited. The difference in effectiveness may relate to selenium sulfide's dual action on both fungal growth and epithelial cell turnover.

For seborrhoeic dermatitis, NICE Clinical Knowledge Summaries recommend antifungal shampoos containing selenium sulfide or ketoconazole as appropriate first-line treatments. Selenium sulfide may be particularly beneficial for more severe cases or when there is significant scalp inflammation, as its cytostatic properties help control the rapid cell proliferation characteristic of this condition.

Speed of action varies between treatments. Selenium sulfide typically produces noticeable improvements within the first few weeks of twice-weekly application. However, individual response varies considerably, and some patients may find one agent more effective than another.

It is important to note that if symptoms persist after 4 weeks of appropriate use, patients should consult their GP, as this may indicate a different underlying condition requiring alternative investigation or treatment. Conditions that may mimic dandruff or seborrhoeic dermatitis include scalp psoriasis, tinea capitis (fungal infection), and certain forms of eczema, each requiring specific management approaches.

Side Effects and Safety Considerations

When used as directed, selenium sulfide is generally well-tolerated, though patients should be aware of potential side effects.

Selenium sulfide can cause several local adverse effects:

• Scalp irritation – burning, stinging, or increased sensitivity

• Hair discolouration – may cause yellowing or orange tinting of grey, blonde, or chemically treated hair

• Oiliness or dryness – some patients experience either increased scalp oiliness or excessive dryness

• Hair loss – rarely, increased hair shedding may occur, though this is typically temporary

• Contact dermatitis – allergic reactions are uncommon but possible

Selenium sulfide should be kept away from the eyes, as it can cause significant irritation. If accidental eye contact occurs, rinse thoroughly with water. The product should not be used on broken or inflamed skin. It should not be used within 48 hours of hair colouring or perming treatments, and can discolour jewellery and fabrics, so thorough rinsing is essential.

Regarding pregnancy and breastfeeding, selenium sulfide should generally be avoided unless clearly necessary, and the benefit outweighs the risk. It should not be applied to the breast during breastfeeding.

Pyrithione zinc, where still available, may cause:

• Mild scalp irritation

• Skin dryness

• Allergic reactions – rare cases of contact dermatitis

• Eye irritation – if product enters eyes during washing

However, as pyrithione zinc is no longer permitted in UK cosmetic products and is not licensed as a medicine, its use is not recommended in the UK context.

Important safety advice: Patients should discontinue use and contact their GP if they experience severe irritation, rash, swelling, or signs of allergic reaction. Neither product should be ingested, and both should be stored out of reach of children.

Patients are encouraged to report any suspected side effects to medicines via the MHRA Yellow Card scheme (website: yellowcard.mhra.gov.uk or search for 'MHRA Yellow Card' in Google Play or Apple App Store).

Which Treatment Is Right for You?

Selecting the most appropriate treatment for scalp conditions depends on several factors, including the severity of your condition, scalp sensitivity, hair type, and treatment goals.

Consider selenium sulfide if you have:

• Moderate to severe dandruff – the stronger cytostatic action may provide better control of heavy flaking

• Seborrhoeic dermatitis with significant inflammation – particularly effective for acute flare-ups

• Persistent symptoms despite other treatments

• Natural dark hair – lower risk of cosmetic discolouration

However, selenium sulfide may not be ideal if you have chemically treated, blonde, or grey hair due to discolouration risk, or if you have very sensitive skin prone to irritation.

Alternative licensed treatments include ketoconazole 2% shampoo, which is often recommended as a first-line treatment for dandruff and seborrhoeic dermatitis in the UK. Coal tar preparations are also available and may be suitable for some patients.

Practical usage recommendations for selenium sulfide: The shampoo should be applied to wet hair, massaged into the scalp, and left on for 2-3 minutes before thoroughly rinsing. Initial treatment typically involves application twice weekly for 2 weeks, followed by once-weekly maintenance if needed. If one treatment is not effective, switching to a different active ingredient may be beneficial.

When to seek medical advice: Contact your GP if:

• Symptoms persist beyond 4 weeks of appropriate treatment

• You develop severe scalp inflammation or significant hair loss

• The condition spreads beyond the scalp or affects the face

• You have a compromised immune system

• There is severe redness, crusting, or pustules on the scalp

• You experience symptoms in a child under 12 years

These may indicate alternative diagnoses such as psoriasis, eczema, or fungal infections requiring different management approaches. NICE guidance recommends considering referral to dermatology for refractory cases or diagnostic uncertainty.

Your community pharmacist can provide additional guidance on selecting the most appropriate option for your specific circumstances, including advice on licensed treatments available in the UK.

Frequently Asked Questions