This is the fourth article in the LJO Explains series — a glossary of cosmetic terms, decoded honestly. Because understanding what is on your label is the first step to understanding what is on your skin.

Your skin communicates constantly — through texture, tone, reactions, and conditions that change with the seasons, your diet, your stress levels, and the products you use. But the vocabulary used to describe these signals can feel clinical, complicated, or simply impenetrable.

Knowing what terms like TEWL, the skin microbiome, or atopic dermatitis actually mean — not just vaguely, but precisely — changes the way you think about your skin and the choices you make for it.

This instalment of LJO Explains decodes the language of skin types and conditions.

Xerosis (Dry Skin)

What it means: Xerosis is the medical term for abnormally dry skin — a condition characterised by a lack of moisture in the stratum corneum (the outermost skin layer). It presents as roughness, flaking, tightness, and sometimes itching or cracking.

Causes: Cold or dry climates, central heating, excessive washing (particularly with harsh surfactants), age-related decline in sebum production, certain medications, and underlying medical conditions including hypothyroidism and diabetes.

Why it matters: Chronic xerosis is not merely uncomfortable — it compromises the skin barrier, making the skin more vulnerable to irritants, allergens, and infections. Restoring moisture and barrier function is the primary therapeutic goal.

Le Joyau d'Olive: Virgin olive oil's emollient and humectant properties — combined with the natural glycerol produced during our cold saponification process — make our soaps particularly suitable for xerosis-prone skin. Unlike synthetic detergents that strip the skin's natural oils, our soaps cleanse while nourishing the barrier they are meant to protect.

Erythema (Redness)

What it means: Erythema is the medical term for redness of the skin caused by increased blood flow to the capillaries — typically in response to irritation, inflammation, UV exposure, heat, or allergic reaction.

Types of erythema:

  • Reactive erythema — a temporary response to an external trigger (sunburn, a hot shower, an irritating ingredient)
  • Chronic erythema — persistent redness associated with conditions like rosacea, eczema, or seborrheic dermatitis

What causes cosmetic-related erythema: Synthetic fragrance, alcohol, certain preservatives, and harsh surfactants are among the most common cosmetic triggers of erythema in sensitive skin.

Le Joyau d'Olive: Our soaps contain no synthetic fragrance, no alcohol, and no synthetic surfactants — the three most common cosmetic triggers of skin redness. The anti-inflammatory properties of virgin olive oil and our pure essential oils actively support the reduction of erythema rather than exacerbating it.

Pruritus (Itching)

What it means: Pruritus is the medical term for itching — a sensation that triggers the urge to scratch. It can be localised (confined to a specific area) or generalised (affecting the whole body), and ranges from mildly irritating to severely debilitating.

Common causes in the context of skincare: Dry skin (xerosis), allergic contact dermatitis (reaction to a cosmetic ingredient), irritant contact dermatitis (damage from harsh products), eczema, psoriasis, and certain fungal infections.

The scratch-itch cycle: Scratching provides momentary relief but damages the skin barrier, releasing inflammatory signals that worsen itching — creating a cycle that is difficult to break without addressing the underlying cause.

Le Joyau d'Olive: Many of our customers with chronic pruritus — particularly those with eczema-prone or sensitive skin — report significant improvement after switching to Le Joyau d'Olive from synthetic detergent soaps. The absence of synthetic fragrance and surfactants, combined with the soothing properties of olive oil and natural glycerol, reduces the triggers that perpetuate the itch-scratch cycle.

Atopic Dermatitis (Eczema)

What it means: Atopic dermatitis — commonly known as eczema — is a chronic inflammatory skin condition characterised by dry, itchy, inflamed skin that periodically flares. It affects approximately 15–20% of children and 1–3% of adults globally.

The underlying mechanism: Atopic dermatitis involves a compromised skin barrier — specifically, a deficiency or dysfunction in filaggrin, a protein essential to the integrity of the stratum corneum. This allows moisture to escape and irritants and allergens to penetrate more easily, triggering the inflammatory immune response that causes flares.

Common triggers: Synthetic fragrance, certain preservatives (particularly methylisothiazolinone), harsh surfactants (SLS/SLES), extremes of temperature, stress, and certain foods.

Le Joyau d'Olive: Dermatologists frequently recommend olive oil-based soap for atopic skin — the fatty acid profile of olive oil closely resembles the natural lipids in the skin barrier, making it one of the most compatible cleansing bases available. Our Olive Breeze (fragrance-free) and Lavender Whisper variants are particularly recommended for eczema-prone skin.

Seborrhoea (Oily Skin)

What it means: Seborrhoea refers to excessive production of sebum — the oily, waxy substance produced by the sebaceous glands. It manifests as oily, shiny skin — typically most pronounced on the face (particularly the T-zone), scalp, and upper back.

The role of sebum: Sebum is not intrinsically negative. It is a critical component of the skin's acid mantle and barrier function — lubricating and waterproofing the skin surface. Excess sebum, however, can contribute to enlarged pores, acne, and certain inflammatory skin conditions.

The counterintuitive approach: Stripping seborrhoeic skin with harsh cleansers can paradoxically worsen the condition — the skin responds to over-cleansing by producing even more sebum. Gentle cleansing that maintains the skin's natural balance is more effective long-term.

Le Joyau d'Olive: Green Tea Mystique and Pine Charisma — both with natural sebostatic properties — are our recommended variants for oily and seborrhoeic skin types. They regulate sebum production without stripping, maintaining balance rather than disrupting it.

Hyperpigmentation

What it means: Hyperpigmentation is a condition in which patches of skin become darker than the surrounding skin due to an overproduction of melanin — the pigment that gives skin its colour. It manifests as age spots, melasma, post-inflammatory hyperpigmentation (PIH), and freckles.

Common causes: Sun exposure (the most significant factor), hormonal changes (particularly during pregnancy — melasma), post-inflammatory responses to acne, eczema, or injury, and certain medications.

Prevention: Daily SPF application is the single most effective preventive measure for UV-induced hyperpigmentation. Antioxidants — particularly vitamin C and the polyphenols in green tea and olive oil — provide additional photoprotective support.

Le Joyau d'Olive: The vitamin E and polyphenols in our soaps provide antioxidant support that helps neutralise UV-induced free radicals — a contributing factor to hyperpigmentation. Our Green Tea Mystique soap, rich in EGCG polyphenols, is particularly relevant for skin prone to uneven tone.

Transepidermal Water Loss (TEWL)

What it means: Transepidermal Water Loss — abbreviated as TEWL — is the process by which water evaporates through the skin to the surrounding environment. It is a normal and constant physiological process. Elevated TEWL, however — measured in grams of water lost per square metre per hour — is a reliable indicator of skin barrier compromise.

Why it matters: When the skin barrier is intact, TEWL is low — the barrier effectively retains moisture. When the barrier is damaged — by harsh cleansers, over-exfoliation, environmental stress, or conditions like eczema — TEWL increases, and the skin loses moisture faster than it can be replaced. This is why moisturisation alone is insufficient without also repairing the barrier.

How skincare products affect TEWL:

  • Occludents — physically reduce TEWL by creating a barrier on the skin surface
  • Emollients — fill gaps in the skin barrier, reducing TEWL indirectly
  • Harsh surfactants — increase TEWL by stripping the barrier lipids

Le Joyau d'Olive: Cold process saponification preserves the emollient fatty acids in olive oil in the finished soap bar — supporting barrier integrity and helping to keep TEWL at healthy levels after washing. This is measurably different from synthetic detergent soaps, which have been shown in clinical studies to significantly increase TEWL.

Skin Microbiome

What it means: The skin microbiome is the complex community of microorganisms — bacteria, fungi, viruses, and mites — that live on and within the skin. Far from being harmful, these microorganisms are essential to skin health: they compete with pathogens, support immune function, maintain the skin's pH, and contribute to barrier integrity.

Key bacteria of the skin microbiome: Staphylococcus epidermidis (protective, dominant on healthy skin), Cutibacterium acnes (associated with acne when in imbalance), Malassezia (associated with dandruff and seborrheic dermatitis in excess).

How modern skincare disrupts the microbiome: Antibacterial soaps, harsh surfactants, and products with a very high or very low pH can dramatically alter the composition of the skin microbiome — reducing microbial diversity and allowing pathogenic species to proliferate. This is increasingly linked to the rising prevalence of eczema, acne, and rosacea.

Le Joyau d'Olive: Unlike antibacterial detergent soaps that indiscriminately target microorganisms, our natural soap — made from olive oil and pure essential oils — supports a healthy microbial balance. The essential oil variants in our collection have selective antimicrobial activity, targeting specific pathogens without wholesale disruption of the beneficial microbiome.

Stratum Corneum

What it means: The stratum corneum is the outermost layer of the epidermis — the visible surface of the skin. It consists of approximately 15–20 layers of flattened, dead skin cells (corneocytes) embedded in a lipid matrix of ceramides, cholesterol, and fatty acids. Despite being composed of dead cells, the stratum corneum is a highly dynamic and functional structure — it is the skin's primary barrier against water loss, UV radiation, microorganisms, and environmental toxins.

Why it matters: The integrity of the stratum corneum determines how well the skin retains moisture, how effectively it excludes irritants and allergens, and how quickly it repairs itself after damage. Almost every skin condition — from xerosis to eczema to acne — involves some degree of stratum corneum dysfunction.

Le Joyau d'Olive: The fatty acid composition of virgin olive oil — particularly its high oleic acid content — is uniquely compatible with the lipid matrix of the stratum corneum. This compatibility means our soaps do not simply cleanse the surface; they actively support the health and integrity of the barrier they are cleaning.

In Summary

Your skin is the body's largest organ — and one of its most communicative. The conditions and reactions it displays are not random; they are signals. Understanding the language in which your skin speaks gives you the ability to respond thoughtfully rather than reactively.

At Le Joyau d'Olive, we formulate with this knowledge at the centre. Every choice — from the base oil to the curing time to the essential oil we select — is made with the health of the skin barrier, the microbiome, and the stratum corneum in mind.

That is what it means to make soap seriously.

This is part of the LJO Explains series — a glossary of cosmetic terms, decoded honestly.
Next in the series: LJO Explains: Greenwashing, INCI Names, Fragrance — The Words the Beauty Industry Doesn't Want You to Understand