Coal Tar and Salicylic Acid for Psoriasis: How They Work

If you've looked into psoriasis treatments, you've almost certainly come across coal tar and salicylic acid. They appear on ingredient labels, in dermatologist recommendations, and in pharmacy aisles. They've been part of psoriasis care longer than most modern prescription drugs have existed.

But knowing that they work is different from understanding why they work. And understanding why opens up something important: these two ingredients don't just treat psoriasis independently — they actively enhance each other. The way they're combined, sequenced, and delivered matters enormously.

This article explains both ingredients from the ground up: the biology of psoriasis they target, how each one acts on the skin, and why the combination outperforms either ingredient alone.

Why Psoriasis Is Hard to Treat Topically

Psoriasis is an autoimmune condition. The immune system sends faulty signals that accelerate the skin cell life cycle from a normal 28–30 days down to just 3–5 days. Cells pile up faster than they can shed, forming the thick, raised, scaly plaques that characterize the condition.¹

This rapid buildup creates two specific challenges for topical treatments:

• Scale acts as a physical barrier. When plaque builds up on the skin surface, it blocks active ingredients from penetrating to where they need to work — the living skin cells underneath.
• Inflammation is ongoing. Even when plaque is cleared, the underlying immune dysfunction continues driving new cell production. Treatment has to address both the surface buildup and the inflammatory process driving it.

Coal tar and salicylic acid each target one of these problems — and used together, they address both simultaneously.

Coal Tar: What It Is and How It Works

Coal tar is a byproduct of coal processing that has been used in dermatology for over 100 years.² It may sound industrial, but it's one of the most studied topical treatments in dermatology — and one of the few non-steroidal options that the American Academy of Dermatology (AAD) explicitly recommends for psoriasis.³

The FDA classifies coal tar as a safe and effective drug ingredient when used in concentrations between 0.5% and 5.0% — meaning products in this range can be sold without a prescription.⁴

How coal tar acts on psoriatic skin

One of the most clinically important properties of coal tar is its ability to increase remission periods — the stretches of time when psoriasis is calm and inactive. The AAD notes that coal tar is particularly useful for scalp psoriasis, where it can both clear active patches and extend time between flares.²

Salicylic Acid: What It Is and How It Works

Salicylic acid is a beta-hydroxy acid (BHA) that has been used in dermatology for well over a century. In psoriasis, its primary function is as a keratolytic — an agent that dissolves and loosens the protein bonds holding dead skin cells together, allowing scale to be removed gently and effectively.

The AAD includes salicylic acid in its non-prescription treatment recommendations for psoriasis, specifically for its scale-softening and scale-removing properties.³

How salicylic acid acts on psoriatic skin

Why Combining Them Works Better Than Either Alone

This is the critical insight that shapes how effective treatment is designed. Coal tar and salicylic acid don't just work independently in parallel — they work sequentially and synergistically.

The logic is straightforward once you understand each ingredient's mechanism:

Coal Tar vs. Steroids: The Long-Term Picture

Topical corticosteroids (steroid creams) are the most commonly prescribed first-line treatment for psoriasis. They work quickly — often showing results within days. But the long-term picture is more complicated, which is why many people seek alternatives like coal tar for ongoing management.

This doesn't mean steroids are never appropriate — they have an important role in managing acute flares, and many dermatologists use them as part of a treatment plan that includes non-steroidal options like coal tar for maintenance. The AAD's clinical guidelines recognize coal tar, salicylic acid, and other topical agents as alternatives or complements to corticosteroid-based treatment.⁵

Safety, Precautions, and Who Should Avoid Them

Both coal tar and salicylic acid have extensive safety records at OTC concentrations. The FDA confirms coal tar is safe and effective between 0.5% and 5.0%.⁴ Salicylic acid is widely used across dermatology with a well-established tolerability profile. That said, there are specific precautions to be aware of:

Coal tar precautions

• Sun sensitivity: Coal tar increases skin sensitivity to UV light. Use sunscreen on treated areas exposed to sunlight, and avoid tanning beds while using coal tar products.²
• Staining: Coal tar can stain clothing, bedding, and light-colored hair. Apply at night and use old linens during treatment.
• Avoid in skin folds and genitals unless specifically directed by a dermatologist — the AAD explicitly advises against applying coal tar to these areas without medical guidance.²
• Pregnancy and breastfeeding: Women who are pregnant or nursing should consult a dermatologist before using coal tar, as there is insufficient data on safety in these cases.²

Salicylic acid precautions

• Use as directed: Overuse — applying to very large body surface areas or too frequently — can cause systemic salicylate absorption, particularly in children. Follow product instructions carefully.
• Avoid on broken or infected skin: Salicylic acid is a keratolytic and can cause irritation if applied to open wounds or infected skin.
• Not for children under 2: Consult a pediatric dermatologist before using salicylic acid products on young children.

Why Delivery Format Changes How Well They Work

The same active ingredient in different formulations can produce very different results. This is especially true for coal tar — because its effectiveness depends heavily on contact time and how deeply it penetrates.

Ointment-based formulas — thick, occlusive vehicles like petrolatum (Vaseline) — are particularly effective for overnight coal tar treatment. The occlusive base slows evaporation, keeps the active ingredient in contact with the skin for hours, and enhances penetration. This extended contact time allows coal tar to work even at lower concentrations — because duration compensates for intensity.

This is also why a two-step system — rinse-off first, leave-on second — is more effective than either format alone. The rinse-off phase removes scale and prepares the skin. The leave-on phase delivers sustained treatment through the night, when skin is in active repair mode.

How Nopsor Applies These Principles

Nopsor was developed by José Luis Aguilar Sánchez, an engineer with a chemistry background who spent years studying topical psoriasis treatments after his own diagnosis. His goal was to create a system that combined the proven science of coal tar and salicylic acid with a delivery approach that maximized their effectiveness — without steroids, without a prescription, and without the rebound effects that complicate long-term steroid use.

The result is a two-step nighttime system built around the synergy described in this article:

• Step 1 — Nopsor Shampoo/Body Wash: Contains salicylic acid to gently exfoliate and lift scale, clearing the surface barrier and dramatically increasing skin permeability. Also contains coal tar at a higher concentration (appropriate for a rinse-off formula) to begin treatment even during the wash phase.
• Step 2 — Nopsor Deep Moisturizing Pomade: An occlusive, petrolatum-based formula containing coal tar and a proprietary blend of eight plant-based botanicals — thyme, rosemary, elderflower, walnut leaf, and four others. The thick vehicle keeps the active ingredients in sustained contact with the now-prepared skin throughout the night. Coal tar concentration is lower here because the contact time is far longer — by design, not by accident.

The eight-herb blend isn't decorative. Each herb was selected for documented skin-calming, anti-inflammatory, or barrier-supporting properties — adding a complementary layer of action on top of the coal tar and salicylic acid foundation. Together, the system addresses psoriasis at every level: surface scale, skin barrier, cell turnover rate, and inflammation.

No steroids. No prescription required. Safe for long-term use.

The Bottom Line

Coal tar and salicylic acid have earned their place in psoriasis treatment not through marketing but through more than a century of clinical use and ongoing research. Coal tar addresses the inflammatory and cell-cycle dysfunction at the root of psoriasis. Salicylic acid clears the scale barrier that prevents any topical treatment from working effectively. Used together in the right sequence and the right delivery format, they produce results that neither achieves alone.

If you're managing psoriasis and looking for a treatment approach that's both evidence-based and sustainable for long-term use, understanding these ingredients — and how they interact — is the most useful place to start.

For a broader view of how psoriasis progresses and the full range of available treatments, see our guide to Scalp Psoriasis: Causes, Treatments & Home Remedies and our overview of Is It Psoriasis or a Skin Allergy?