The Saint Louis ointment is a magistral preparation made in pharmacies, primarily composed of ichthyol, petroleum jelly, lanolin, boric acid, and coal tar. Its name refers to an old formula, still prescribed by some dermatologists to treat skin conditions such as psoriasis or diaper rash in infants.
Ichthyol and coal tar: two active ingredients with complementary properties
The composition of the Saint Louis ointment is based on a simple principle: combining substances with anti-inflammatory and keratolytic properties in a fatty excipient. Ichthyol (or pale ichthyol) is a derivative of bituminous shales used since the late 19th century in dermatology. It acts on local inflammation and helps reduce redness.
Coal tar, the second characteristic active ingredient of this formula, has antipruritic and anti-scaling properties. On skin thickened by psoriasis, it helps slow down the excessive cell proliferation that forms plaques. The combination of these two substances in the same topical treatment targets both inflammation and scaling.
The fatty base (petroleum jelly and lanolin) plays a significant role: it forms an occlusive film that maintains hydration of the stratum corneum. To better understand the use of Saint Louis ointment, it is important to keep in mind that this ointment formulation is specifically intended for dry and scaly lesions, not for weeping areas.
Boric acid, present in small amounts, provides a slight antiseptic effect. Its concentration in the formula remains limited, which explains why the ointment does not replace antibacterial treatment in the case of a declared skin infection.
Saint Louis ointment for psoriasis: what it treats and what it does not
Psoriasis is the most frequently associated indication for this preparation. The dry, thick plaques on elbows, knees, or the scalp respond well to the combined action of coal tar and ichthyol. The improvement concerns the symptoms, not the underlying cause. Psoriasis is a chronic inflammatory disease with an immune component: no topical treatment cures it.
In practice, the first visible results (reduction in plaque thickness, decrease in itching) generally appear after one to two weeks of regular application. This timeframe is consistent with what is observed for other topical treatments for psoriasis.
The Saint Louis ointment shows its limits on extensive forms. When plaques cover a significant body surface area, a dermatologist will likely recommend appropriate class local corticosteroids, phototherapy, or systemic treatments. The ointment remains relevant for localized areas, as a complement or a follow-up to a more potent treatment.
The case of diaper rash in infants
Some pediatricians prescribe Saint Louis ointment for diaper rashes resistant to conventional diaper creams. The barrier effect of petroleum jelly protects irritated skin from contact with urine, while ichthyol soothes inflammation. This use remains regulated by a prescription: the formula contains coal tar, an active ingredient whose use in infants should be limited in duration and surface area.
Detailed composition and differences between pharmacies
Since it is a magistral preparation, the Saint Louis ointment is not an industrial drug with a standardized formula at the national level. Each compounding pharmacy can slightly adjust the proportions according to the physician’s prescription. The common base remains:
- Ichthyol (pale or sodium): main anti-inflammatory agent, responsible for the dark color of the product
- Coal tar: keratolytic and antipruritic active ingredient, with a characteristic odor
- Petroleum jelly and lanolin: fatty excipients that ensure the occlusive effect and facilitate application
- Boric acid: mild antiseptic in moderate concentration
This variability between pharmacies explains why two tubes bearing the same name may differ in texture or color. The shade varies from dark brown to black depending on the coal tar dosage. The odor, often described as strong and persistent, is one of the most frequently cited drawbacks by users.
User reviews on Saint Louis ointment: recurring trends
The feedback shared on health forums and patient communities paints a fairly consistent profile. Three points regularly emerge:
- The effectiveness on localized psoriasis plaques is often deemed satisfactory, with a notable decrease in scales and itching after a few days
- The thick texture and dark color stain clothing and bedding, complicating daily adherence
- The coal tar odor divides opinions: some patients accept it as a compromise for effectiveness, while others abandon treatment for this sole reason
In terms of tolerance, irritations remain rare when the ointment is applied to dry lesions as prescribed. Reactions mainly occur when applied to broken or weeping skin, a situation for which the ointment formulation is not suitable.
Application routine and precautions
Application is generally done once or twice a day, in a thin layer on the affected areas. An occlusive dressing may be used on prescription to enhance the penetration of the active ingredients, but this technique also increases the risk of local irritation.
The duration of treatment should remain limited in time, especially on areas of thin skin (folds, face). Coal tar is an active ingredient whose prolonged use without medical supervision is not recommended. A dermatological check-up after a few weeks allows for evaluating the response and adjusting the management.
The Saint Louis ointment holds a place in the dermatological arsenal for localized dry lesions, provided one accepts its cosmetic constraints. Its status as a magistral preparation means it is not available over the counter: a prescription and a pharmacy equipped for compounding are the two prerequisites for obtaining it.