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The glow is optical, not chemical. Three mechanisms, often combined:

Mechanism	Ingredient	Effect
Specular reflection	Mica platelets, synthetic fluorphlogopite	A directional sheen; the platelets align flat on the skin
Interference / pearlescence	Mica or borosilicate coated with titanium dioxide or iron oxide	Colour that shifts with viewing angle — the "duochrome" effect
Diffusion	Fine silica, boron nitride, PMMA spheres	A soft blur rather than a sparkle

Coated mica is the workhorse. A thin layer of titanium dioxide on a transparent platelet produces thin-film interference, the same physics that colours a soap bubble: the apparent colour depends on the coating thickness and the angle of view. That is why an expensive highlighter shifts from champagne to pink to green as the head turns, and a cheap one just glitters.

Synthetic fluorphlogopite — "synthetic mica" — is worth knowing by name. It is a lab-grown analogue with a more uniform platelet and a cleaner supply chain.

A substantial share of natural cosmetic-grade mica has historically come from sheet-mica belts in India and Madagascar, where child labour in informal mining is a documented and persistent problem. The industry response has been supply-chain initiatives, traceability programmes, and a shift toward synthetic fluorphlogopite.

Neither the FD&C Act nor Regulation (EC) No 1223/2009 addresses labour conditions; this is outside the cosmetic rule books entirely and sits with supply chain and modern-slavery legislation. Synthetic mica sidesteps it, and a brand naming synthetic fluorphlogopite on the label is telling you something real.

• Only on what should catch light: the top of the cheekbone, the brow bone, the inner corner, the bridge of the nose, the cupid's bow, the collarbone.
• Texture is amplified. A shimmering particle sitting in a pore or a fine line makes it more visible, not less. On textured or mature skin, a satin or diffused finish beats a metallic one.
• Powder over powder, cream over cream. A powder highlighter dragged over a wet cream base grabs.
• Not over active acne — shimmer draws the eye directly to raised texture.
• Flash photography exaggerates it several times over.

Liquid and cream highlighters mixed into foundation give a whole-face glow that reads as skin rather than product.

Cosmetic — FDA primary category (08), makeup preparations (not eye), or (03) for anything used on the eye area. Colour additives must be approved for the intended area of use, which matters here because highlighters are routinely used on the brow bone and inner corner: pigments not approved for eye-area use may not be present in a product intended there.

Certified colours must come from FDA-certified batches. Mica, titanium dioxide, iron oxides and bismuth oxychloride are exempt from batch certification but must still be approved for the use.

Bismuth oxychloride deserves a note: it produces a distinctive pearly finish and is a recognised irritant for a minority of users, causing itching and small bumps that get mistaken for a breakout.

Powder: 18–24 months after opening. Cream and liquid: 12 months. Pressed highlighters develop the usual hard glaze from brushes carrying sebum back into the pan — scrape rather than dig. Baked and cream-to-powder formats crack when dropped, which is cosmetic damage rather than spoilage.

• Makeup — the shelf this sits on, and the rest of it.
• Cosmetics — what the label is legally allowed to say, and the full catalogue.
• The rest of Colour and contour — Blush · Bronzer · Contour · Face Paint · Body Paint · Leg Makeup.
• Body Glitter — the same optics, much larger particles.
• Regulatory statements here follow the FDA and EU sources listed on Cosmetics, read 16 August 2026.