Ingredient Glossary · Essential Oils

Bergamot Essential Oil

Citrus bergamia Risso et Poiteau · Calabria PDO

A comprehensive scientific and perfumery reference — covering chemistry, grades, phototoxicity, Calabrian PDO, linalyl acetate authentication, and Chypre and Fougère formulation for Pakistani formulators.

Calabria
PDO Origin
Restricted
IFRA Status
1–3 yr
Shelf Life
Scroll
Quick Reference

At a Glance

Botanical Name
Citrus bergamia Risso et Poiteau
Family
Rutaceae — Citrus / Rue family
CAS Number
8007-75-8 (cold-pressed) · 68648-33-9 (FCF)
Plant Part
Fresh peel (rind) of ripe fruit — cold-press expression
Extraction
Cold-press expression (commercial standard) · ISO 3520:2011
Appearance
Pale greenish-yellow to yellowish mobile liquid
Specific Gravity
0.875–0.880 @ 20°C
Flash Point
~62°C · Refractive Index: 1.464–1.468 @ 20°C
Odour Profile
Fresh sparkling citrus with distinctive floral-neroli facet; sweet, slightly spicy; clean woody drydown
Major Constituents
Limonene 32–42%, Linalyl Acetate 26–38%, Linalool 5–12%, γ-Terpinene 5–8%
IFRA Status
Restricted (cold-pressed). FCF grade significantly more permissive. Use FCF for all leave-on skin products.
Key Regions
Calabria Italy (PDO standard); Ivory Coast; Brazil; Argentina; Turkey
Phototoxicity
Cold-pressed: phototoxic (bergapten 0.2–0.5%). FCF grade: bergapten <10ppm, safe for leave-on use.
Shelf Life
1–3 years sealed · 6–12 months opened · refrigerate; monitor for terpene oxidation
Introduction

The Perfumer's Most Used Citrus

Bergamot essential oil — cold-pressed from the ripe peel of Citrus bergamia, a fruit grown almost exclusively in the narrow coastal strip of Calabria in southern Italy — occupies a unique place in fragrance that is simultaneously universal and unrecognised. Present in an estimated 35–50% of all men's fine fragrances and the structural top note of both the Fougère and Chypre families, bergamot is arguably the single most commercially important natural essential oil in fine fragrance globally. What elevates it above every other citrus oil is its unusually high linalyl acetate content (26–38%) — the ester that bridges bergamot compositionally between the citrus and floral families, giving it a sweetness and floral complexity no other citrus oil can match.


For Pakistani formulators, bergamot is essential knowledge across multiple market segments: the bergamot-oud pairing defines contemporary Gulf and Pakistani luxury fragrance; bergamot FCF (Furanocoumarin-Free / bergapten-free) enables premium natural skin care with documented antimicrobial and anti-inflammatory activity; and bergamot's growing recognition through Earl Grey tea creates fresh market positioning opportunities in home fragrance and wellness. The critical distinction is always grade — standard cold-pressed for fine fragrance, and FCF mandatory for any leave-on skin product.

Bio Shop™ Pakistan — Sourcing Note

We supply two bergamot grades: Cold-Pressed Bergamot (standard Calabrian) — for fine fragrance, diffusion, and rinse-off products — and Bergamot FCF (bergapten-free), the mandatory grade for any leave-on skin care product. Both available with full GC/MS documentation. Always specify which grade you require. Order at bioshop.pk

Botanical Identity

Taxonomic Classification

KingdomPlantae
OrderSapindales
FamilyRutaceae — Citrus / Rue family
GenusCitrus L.
SpeciesCitrus bergamia Risso et Poiteau
SynonymsCitrus aurantium ssp. bergamia
Common NamesBergamot Orange · Prince's Pear
Urdu / PakistanBergamot (no traditional Urdu name) — borrowed as بیرگاموٹ
PDO StatusProtected Designation of Origin — Calabria, Italy only
ISO StandardISO 3520:2011 — Oil of Bergamot
Two Key GradesCold-Pressed Standard (bergapten present) · FCF / bergapten-free (leave-on safe)
Production Volume~100–150 tonnes/year Calabrian PDO — genuine supply scarcity creates premium
Grade Intelligence

The Four Bergamot Grades

Always specify grade when ordering. Verify bergapten content on your Certificate of Analysis for any leave-on skin application. For fine fragrance and diffusion, standard cold-pressed Calabrian is the gold standard. For skin contact, FCF is mandatory.

Cold-Pressed · PDO
Calabrian Standard
Calabria, Italy — Fine Fragrance Benchmark
Linalyl Acetate
26–38%
Highest LA content — full floral-citrus complexity
"Sparkling, luminous freshness with unmistakable floral-neroli lift; sweet heart; warm barely-there drydown — the definitive fine fragrance citrus opening."
Cold-Pressed · FCF · Skin-Safe
Bergamot FCF
Calabrian origin · bergapten molecularly removed
Bergapten Content
<10 ppm
Mandatory for ALL leave-on skin products
"Virtually identical to standard grade — very slight reduction in deepest base nuance. Fully acceptable for all applications. The only choice for attar, body oil, serum, and lotion."
Cold-Pressed · Commodity
Ivory Coast
West Africa — Commercial Volume Grade
Linalyl Acetate
18–28%
Higher limonene, less floral depth than Calabrian
"Bright, sharper citrus; less floral complexity; good commercial quality for functional products and lower-cost fragrance. Linalool/LA ratio significantly different from Calabrian."
Steam-Distilled
Steam-Distilled
Various origins — Naturally bergapten-free
Quality vs Cold-Pressed
Inferior
Naturally phototoxic-free · aromatically flatter
"Less bright than cold-pressed; flatter citrus with less zest and far less floral complexity. Use only when phototoxicity avoidance is prioritised over aromatic quality."
GC/MS Data

Chemical Composition

Typical constituent ranges for Calabrian cold-pressed bergamot. GC/MS verification per batch strongly recommended. Non-Calabrian origins will show significantly lower linalyl acetate. The linalyl acetate / linalool ratio is the primary Calabrian authentication index.

Limonene32–42%
Dominant monoterpene — crisp fresh citrus backbone; primary stability concern due to oxidation susceptibility forming harshly smelling hydroperoxides on exposure to air and heat
Linalyl Acetate26–38%
The defining quality marker — floral, sweet, fruity; bridges bergamot between citrus and floral families; primary adulteration target; ratio to linalool is the Calabrian authentication fingerprint
Linalool5–12%
Soft, floral-woody oxygenated monoterpene — partner to linalyl acetate; linalool/LA ratio (~0.25–0.35 for Calabrian) is a key authentication index; EU declared allergen
γ-Terpinene5–8%
Citrus-herbal, slightly peppery — background freshness; characteristic of citrus oils; susceptible to oxidation on storage
β-Pinene4–7%
Fresh, woody-pine, slightly citrus — structural modifier in the fresh top note character; contributes diffusive brightness
α-Pinene1–3%
Clean, pine-fresh, resinous — uplifting minor top note contributor; antimicrobial activity; common to most citrus oils
Myrcene1–3%
Green, slightly musky-tropical — bridges citrus to herbal character; contributes to the complex opening impression
Geranial (Citral A)0.3–1%
Fresh lemon, powerful at very low concentration; low odour detection threshold; contributes the characteristic bergamot-like citrus nuance
Geraniol0.3–1%
Rose-geranium, floral — minor aromatic contribution; EU declared allergen at threshold concentrations; declaration required in leave-on formulations
β-Bisabolene0.2–0.8%
Warm, slightly woody-balsamic sesquiterpene — minor base note unique to bergamot among citrus oils; contributes lingering warmth in the drydown
Bergapten (cold-pressed only)0.2–0.5% · PHOTOTOXIC
SAFETY CRITICAL — furanocoumarin causing Berloque dermatitis (persistent hyperpigmentation) on UV-exposed skin; completely ABSENT in FCF grade; primary IFRA restriction driver for bergamot
Sabinene0.5–1.5%
Spicy, woody-citrus — minor structural contributor; anti-inflammatory activity reported; common minor component in citrus peel oils
Sensory Analysis

Olfactory Evolution

Top Note · 0–30 min
Opening
Sparkling, luminous citrus brightness driven by limonene and pinenes. Linalyl acetate immediately adds a distinctive floral-neroli lift that separates bergamot from every other citrus oil — a lightness and complexity no lemon, orange, or grapefruit can replicate.
Heart Note · 30 min – 3 hrs
Heart
Soft, sweet floral character dominated by linalyl acetate — reminiscent of neroli but warmer, more citrus-grounded. Subtle spicy-herbal undertone from γ-terpinene. The oil's most complex and beautiful phase; this is why bergamot is irreplaceable in fine fragrance.
Drydown · 3+ hrs
Drydown
β-bisabolene and α-bergamotene contribute a faint warm, woody-balsamic depth. Quality Calabrian bergamot leaves a warm, slightly floral-musky impression long after the initial brightness fades. In Pakistani summer heat, the opening is dramatic but brief — anchor with cedarwood or patchouli for longevity.
Descriptor Vocabulary
sparkling citrus floral-neroli lift sweet-linalic luminous fresh slightly spicy clean warm drydown balsamic-woody hesperidic transparent Earl Grey citrus-floral elegant
Perfumery Practice

Accord Formulas

Two professional starter formulas — a Pakistani luxury attar and a contemporary Chypre EDP. Always use FCF bergamot for leave-on skin products. Calculate total regulated constituents against current IFRA standards before production.

Subah-e-Oud — Pakistani Fresh Oriental Attar
FCF Bergamot · DPG Carrier · 100% Natural · Fully Halal · No Alcohol
Rose Absolute (Turkish or Bulgarian)10.0g 10%
Oud accord / Plantation Oud EO6.0g 6%
Saffron CO₂ Extract (Zafran)2.0g 2%
Labdanum Absolute5.0g 5%
Amber Accord (natural resin blend)7.0g 7%
🌟 FCF bergamot MANDATORY for leave-on attar wear. Verify bergapten <10 ppm on COA. Blend all aroma ingredients together first, then use in DPG or as a neat concentrated attar. For a DPG-diluted pulse-point attar, take 20g of this compound and add 80g DPG. Mature 72 hours minimum — the bergamot-oud marriage needs time. Structure: bergamot-rose top → frankincense-cardamom heart → patchouli-vetiver-amber base. Total compound: 100g.
Contemporary Natural Chypre — EDP Spray
Bergamot FCF · Bio Shop™ Perfume Premix · 20% Concentration EDP
Step 1 — Fragrance Compound (100g total):
Rose Absolute12.0g 12%
Labdanum Absolute8.0g 8%
Oakwood accord (modern oakmoss alternative)5.0g 5%
Step 2 — 30ml Spray Bottle Assembly:
Fragrance Compound (Step 1)6ml 20%
🍋 Perfume Premix = sole alcohol base. Bio Shop™ Perfume Premix is ready-to-use Perfumers Alcohol — no additional fixative calculation needed. Blend compound fully before adding to Premix. Shake gently. Maturation: Minimum 3 weeks; 6 weeks ideal — the bergamot-patchouli Chypre tension requires time to resolve into harmony. Structure: bergamot-lemon-neroli top → rose-geranium heart → patchouli-labdanum-vetiver-oakwood base. A fully natural Chypre structure. Expected longevity: 6–9 hours on skin.
Blending Guide

Classical Pairings

Fougère family — bergamot as fresh masculine opening
Chypre family — bergamot over dark mossy-earthy base
Oriental / Pakistani luxury — bergamot as luminous opening
Citrus accord — layering freshness and complexity
Material Intelligence

Similar Materials

Lemon EO → Shop
Limonene 55–70%, Citral 3–8%, Linalyl Acetate <2%
Aroma
Very bright, sharp, clean citrus; less floral
Best Use
Bright sharp citrus applications
vs. Bergamot: Sharper, more purely citrus; significantly less floral complexity; bergamot preferred in fine fragrance for depth and sophistication. Lemon is more affordable and accessible; bergamot more refined. Excellent together in citrus top notes.
Neroli EO → Shop
Linalool 30–40%, Linalyl Acetate 5–10%, Farnesol trace
Aroma
Intensely floral-citrus, honeyed, orange blossom
Best Use
Precious floral-citrus, Eau de Cologne
vs. Bergamot: Shares citrus-floral territory; neroli more intensely floral and precious; bergamot fresher and more citrus-forward. Exceptional pairing together — neroli adds depth and honeyed richness while bergamot provides the clean sparkling opening.
Petitgrain EO → Shop
Linalyl Acetate 40–55%, Linalool 15–25%
Aroma
Green, woody-citrus, slightly bitter-herbal
Best Use
Green citrus, masculine accords
vs. Bergamot: Share linalyl acetate/linalool chemistry; petitgrain greener, drier, more bitter; bergamot brighter and more purely citrus-floral. Excellent pairing for citrus complexity — petitgrain dramatically extends bergamot's volatile top note presence.
Lavender EO → Shop
Linalyl Acetate 35–50%, Linalool 25–40%
Aroma
Floral, clean, slightly herbal, calming
Best Use
Fougère family; skin care
vs. Bergamot: The two premier linalyl acetate oils — defining pairing of the Fougère family. Lavender rounder and more floral; bergamot bright and citrus-led. Extraordinary compatibility — together they create the most universally appealing men's fragrance opening possible.
Sweet Orange EO
Limonene 90–95%, minimal other compounds
Aroma
Sweet, familiar, simple, direct
Best Use
Accessible sweet citrus; cleaning products
vs. Bergamot: Simplest citrus top note; incomparably less complex than bergamot; used for accessible sweetness, not sophistication. Orange degrades very rapidly due to high limonene with no supporting esters; bergamot is far more stable.
Grapefruit EO
Limonene 85–95%, Nootkatone trace
Aroma
Clean, bitter-fresh, slightly metallic citrus
Best Use
Clean-sharp citrus opening; wellness products
vs. Bergamot: Sharper and more bitter; bergamot far more versatile and elegant in combination; grapefruit for clean-sharp applications only. Neither is versatile enough alone — bergamot + grapefruit creates a modern clean-citrus accord with more dimension than either alone.
Regulatory & Safety

IFRA, Phototoxicity & Safety

Important Disclaimer: General educational guidance only. Bio Shop™ Pakistan does not provide regulatory or safety consultancy. Consult current IFRA standards (ifrafragrance.org), EU Cosmetic Products Regulation (CPR 1223/2009), and applicable Pakistani regulations (DRAP, PFA). All safety assessments must be conducted by qualified professionals.
☀️

Phototoxicity — Bergapten

Cold-pressed bergamot contains bergapten (0.2–0.5%), a furanocoumarin that causes Berloque dermatitis — persistent hyperpigmentation on skin exposed to UV after oil application. IFRA maximum: 0.4% in leave-on Category 4 products. Use FCF grade (<10 ppm bergapten) for ALL leave-on skin applications without restriction. FCF grade brings the leave-on limit up to approximately 31% — fully practical for any formulation.

⚠️

Limonene — Primary EU Allergen

Limonene (32–42% in bergamot) is a declared EU CPR allergen. Declare in leave-on products above 0.001%, rinse-off above 0.01%. Limonene hydroperoxides from oxidation are potent sensitisers — proper storage is essential. At typical fine fragrance usage (5–15%), limonene declaration is mandatory in all EU-targeted products.

🌸

Linalool — Declared Allergen

Linalool (5–12%) also requires EU CPR declaration at the same thresholds. Linalool oxidation products (hydroperoxides) are sensitising — store in amber glass away from heat and oxygen to minimise oxidation. In fine fragrance use where bergamot is at 10–20%, linalool declaration is likely required.

FCF Grade — Skin Safe

Bergamot FCF with confirmed bergapten <10 ppm is the correct and legally safer grade for all leave-on skin applications. The IFRA limit increases dramatically vs standard grade. Always document FCF grade and its bergapten COA value in your product safety assessment file. Bio Shop™ supplies FCF grade with full documentation.

💧

Rinse-Off Products

Both standard and FCF grades are very safe in rinse-off applications (shampoo, shower gel, soap) where exposure is transient. Use at 1–3% without meaningful restriction concern. IFRA effectively places no practical limit on standard bergamot in rinse-off categories. Cold-pressed standard bergamot is perfectly appropriate for soaps, shampoos, and body washes.

☪️

Halal Status — Fully Halal

Bergamot essential oil is fully halal — a pure plant extract produced by cold-press expression of citrus peel with no haram inputs at any stage of manufacture. No animal-derived components, no ethanol in production. For halal-certified product development, ensure all other ingredients (carriers, emulsifiers, preservatives) are also halal-compliant. The bright, clean, citrus-floral character aligns well with Islamic aesthetic preference for pleasant, clean, tayyibat fragrances.

Handling & Stability

Storage Guide

Light
Amber or UV-opaque glass mandatory. UV catalyses limonene and terpene oxidation forming harsh off-notes. Never store in clear glass or transparent plastic.
Temperature
Refrigerated (4–10°C) is ideal. Cool room (15–20°C) for short-term. Never above 25°C. Pakistan summers (35–47°C) rapidly degrade quality — opened bergamot in summer can deteriorate within 2–3 months.
Oxygen
Primary degradation driver. Fill to minimum headspace or use inert gas spray before resealing. Transfer to smaller containers as product is used. Nitrogen blanket for bulk storage.
Container
Amber glass preferred. HDPE acceptable short-term. Never aluminium (reactive with citrus acids). Never clear glass. Ensure cap seals are airtight after every opening.
Lahore Storage
Temperatures reach 47–48°C in June–July. Refrigerator storage essential for opened bottles. An unrefrigerated opened bottle in Lahore summer deteriorates to unusable quality within 2 months. Vegetable compartment of fridge (4–8°C) is ideal.
Karachi Storage
High humidity (70–90%) plus 38–42°C summer heat creates dual pressure — heat accelerates limonene oxidation while humidity promotes linalyl acetate hydrolysis. Airtight amber glass + refrigerator mandatory. Check seals for coastal salt air corrosion.
Antioxidant
0.1% BHT or 0.5% mixed tocopherols (Vitamin E) significantly extend shelf life by interrupting free radical autoxidation of limonene. Particularly worthwhile for bulk stock held over Pakistan summer.
Shelf Life
Sealed refrigerated: 18–24 months at full quality. Opened at room temp: 6–12 months standard conditions; 2–4 months in Pakistani summer. Note: bergamot does NOT improve with age — any change over time is deterioration.
Signs of Deterioration: Harsh, resinous or turpentine-like top notes (limonene oxidation products) · Loss of floral freshness · Reduced brightness · Possible rancid off-notes. Once oxidation off-notes are present they cannot be reversed — withdraw from fine fragrance use. Compare against a fresh reference sample before every production batch. In Pakistani summer conditions, smell your bergamot before every use.
Technical Questions

Frequently Asked

What is the difference between bergamot standard, bergamot FCF, and steam-distilled bergamot?+
Standard cold-pressed bergamot (contains bergapten): Use in fine fragrance, rinse-off products (soaps, shampoos, shower gels), diffusion blends, candles — any application where product does not remain on sun-exposed skin. The finest aromatic quality; the benchmark for fine fragrance. Bergamot FCF (cold-pressed, bergapten removed by molecular distillation): Use in ALL leave-on skin care — body oils, face serums, lotions, attar/perfume oils worn on skin. Aromatically nearly identical to standard grade. Mandatory for leave-on skin care. Steam-distilled bergamot: Naturally bergapten-free but aromatically inferior — flatter, less complex. Use only where phototoxicity avoidance is prioritised over aromatic quality. Not suitable for fine fragrance.
How do I detect adulterated or non-Calabrian bergamot on GC/MS?+
Three primary authentication parameters: (1) Linalyl acetate content — genuine Calabrian shows 26–38%; non-Calabrian origins show 15–28%; adulteration with synthetic LA can inflate this figure but chiral analysis reveals racemic distribution. (2) The linalool/linalyl acetate ratio — authentic Calabrian shows approximately 0.25–0.35 (meaning linalool is 25–35% of the LA concentration). LA = 30%, linalool = 10% → ratio 0.33 = Calabrian-consistent. LA = 20%, linalool = 13% → ratio 0.65 = non-Italian origin or blending. (3) Minor sesquiterpene profile — bergamotene and bisabolene at specific levels in authentic Calabrian material; reduced in reconstructed oil. Chiral GC is the definitive adulteration test: natural linalool is predominantly R-(−)-linalool; synthetic additions are racemic.
Why does my bergamot smell harsh or turpentine-like after opening?+
Classic limonene oxidation — the primary degradation pathway for bergamot and all citrus oils. Limonene reacts with atmospheric oxygen to form hydroperoxide and carbonyl compounds (carvone, carveol, limonene epoxide) that produce progressively harsh, resinous, turpentine-like off-notes. Prevention: immediately after opening, minimise headspace, use inert gas blanket, store in amber glass at refrigerated temperatures, add 0.1% BHT or 0.5% tocopherol. Pakistan-specific warning: hot, poorly ventilated storage during summer can degrade opened bergamot to unusable quality within 2–3 months. Always smell bergamot before use and compare against a fresh reference sample. Once oxidation off-notes are present, they cannot be reversed — withdraw from fine fragrance use.
What concentration of bergamot should I use in a Pakistani attar (perfume oil)?+
For attar-format perfume oils, bergamot FCF at 12–20% of total concentrate provides the fresh, clean opening note that elevates traditional oriental formulas for modern urban consumers. Below 12% and the bergamot top note is lost in oriental base notes; above 25% and the citrus character can become too dominant. Recommended: 15–18% for a strong, beautiful opening that transitions gracefully into rose-oud-sandalwood base. For traditional attars targeting conservative consumers, reduce to 8–12% as a freshness modifier. For modern attars targeting urban millennials, use 20–22% as a featured citrus-opening note — what the Subah-e-Oud formula achieves.
How does bergamot function in the Fougère and Chypre fragrance families?+
In the Fougère family (the dominant men's fragrance structure globally), bergamot provides the fresh, clean, citrus-floral opening that makes Fougères immediately accessible and universally appealing — contrasting with lavender's floral warmth and coumarin's sweet base. In the Chypre family, bergamot's bright citrus-floral top note creates the defining aromatic tension against the dark, earthy patchouli-labdanum base — drawing consumers in with freshness before the deeper, more complex base notes emerge. Both families rely on bergamot as the fresh contrast ingredient that prevents opening notes from being too dense. For Pakistani perfumers, a premium natural Fougère (bergamot FCF + lavender + coumarin + cedarwood) represents a significant commercial opportunity in urban professional men's fragrance.
Is bergamot essential oil halal?+
Yes — bergamot essential oil, being a plant-derived aromatic material extracted by cold-press expression without alcohol or animal-derived processing aids, is inherently permissible (halal) under Islamic jurisprudence. For halal-certified product development, the bergamot oil is halal by origin and process; ensure all other ingredients (carriers, emulsifiers, preservatives) are also halal-compliant. Bergamot FCF is particularly suitable for Islamic-positioned premium skin care because it enables high-quality natural fragrance in leave-on products without phototoxicity restriction. The bright, clean, citrus-floral character aligns well with Islamic aesthetic preference for pleasant, clean, natural fragrances (tayyibat).
What is the linalyl acetate/linalool ratio and how do I interpret it on a COA?+
The ratio (linalool ÷ linalyl acetate) — known in Italian quality assessment as the 'grado di essenza' — is the most diagnostically important authentication index beyond total linalyl acetate content alone. Authentic Calabrian bergamot shows ratio approximately 0.25–0.35. Non-Italian origins (particularly Tunisian bergamot) show higher ratios (0.5–0.7) because their biosynthetic pathway produces relatively more linalool than linalyl acetate. On a COA: LA = 30%, linalool = 10% → ratio 0.33 = Calabrian-consistent. LA = 20%, linalool = 13% → ratio 0.65 = likely non-Italian origin or blending. This allows informed sourcing decisions without requiring full chiral GC analysis for routine quality checking.
Why is Calabrian bergamot more expensive than Ivory Coast bergamot?+
Three factors drive the Calabrian premium: (1) Geography — genuine PDO Calabrian bergamot can only be produced in a ~100km coastal strip of southern Italy; total production is only ~100–150 tonnes per year globally, creating genuine supply scarcity. (2) Chemistry — Calabrian bergamot consistently produces 26–38% linalyl acetate; Ivory Coast typically shows 18–28% LA with a measurably less floral, less complex aromatic profile that experienced perfumers immediately detect. (3) PDO protection — like Champagne for wine, Calabrian bergamot has Protected Designation of Origin status. For fine fragrance applications, the Calabrian premium is justified by the aromatic quality difference; for functional or mass-market applications, Ivory Coast bergamot may represent better value.
Full Reference Document

Dive Deeper — Read the Complete Guide

Everything on this page and more — complete Calabrian PDO history, adulteration detection with chiral GC methodology, advanced formulation strategies for bergamot in Pakistani market products, full cultivation and post-harvest processing detail, and Pakistani market opportunity analysis — compiled into one comprehensive reference document.