Short answer
IFRA restricts phototoxic materials — expressed bergamot, lemon, lime, grapefruit and bitter orange oils, angelica root, cumin, rue and a few others — in products left on sun-exposed skin. When a formula contains more than one furocoumarin-containing natural, each one's level must be expressed as a percentage of its own limit in the finished product, and those percentages added: the total may not exceed 100. A formula can therefore fail even when every oil is individually under its limit. The rule applies only to the furocoumarin-containing naturals, not to the other phototoxic materials, and not to products with no skin contact.
What phototoxicity is
Some materials make skin react to ultraviolet light: a perfume applied to the neck and then exposed to sun can leave redness and, later, dark patches where it was sprayed. In citrus and some other plant oils the cause is a group of compounds called furocoumarins, bergapten (5-methoxypsoralen) the best known. Cold-pressed (expressed) citrus oils carry them; distilled oils and grades with furocoumarins removed carry much less. The chemistry and the material choices are in citrus oils in perfumery.
Which materials IFRA restricts for phototoxicity
IFRA's guidance divides them into two groups.
| Group | Materials | Combination rule applies? |
|---|---|---|
| Phototoxic because of furocoumarins they contain | Angelica root oil; bergamot oil expressed; bitter orange peel oil expressed; cumin oil; grapefruit oil expressed; lemon oil cold expressed; lime oil expressed; rue oil; and a Standard on "citrus oils and other furocoumarins containing essential oils" | Yes |
| Phototoxic in themselves | AHMI; methyl N-methyl anthranilate; methyl β-naphthyl ketone; tagetes oil and absolute; methyl 2-(formylamino)benzoate | No — each is checked against its own Standard |
The limits themselves are in the Standards, which IFRA publishes; they are not reproduced here. Read the current Standard for each material, and note that IFRA's guidance says an update of its furocoumarin policy is foreseen for the 52nd Amendment.
Which products it applies to
Phototoxicity restrictions apply to products used on body areas reasonably expected to be exposed to sunlight. IFRA's guidance treats the categories as follows:
- Leave-on for phototoxicity: Categories 1–5, 7B, 8, 10B and 11B.
- Rinse-off for phototoxicity: Categories 6, 7A, 9 and 10A — traditionally unrestricted, though IFRA has begun introducing rinse-off limits for some phototoxic materials as their Standards are revised.
- Not applicable: Category 11A (skin contact without UV exposure) and Category 12 (no skin contact) — candles, diffusers and the like.
The citrus Standards' limits are, in practice, a fine-fragrance and leave-on-products question. For category definitions see IFRA Standards explained.
The combination rule
IFRA's guidance states that if combinations of furocoumarin-containing phototoxic ingredients are used, use levels must be reduced accordingly: the sum of the concentrations of all furocoumarin-containing phototoxic ingredients, each expressed as a percentage of its maximum level in the consumer product, shall not exceed 100.
Written as a calculation:
Σ (level of oil i in the product ÷ limit for oil i) × 100 ≤ 100
Levels and limits are both in the finished product. If your formula records the oils as a percentage of the concentrate, convert first: level in product = level in concentrate × concentrate in product ÷ 100 (how to check IFRA limits works through the conversion).
A worked example
An eau de parfum at 15% concentrate. The limits below are invented for the arithmetic; they are not IFRA's figures.
| Oil | % in concentrate | % in product | Invented limit (%) | % of limit |
|---|---|---|---|---|
| Bergamot oil expressed | 1.20 | 0.180 | 0.40 | 45.0 |
| Lemon oil cold expressed | 2.00 | 0.300 | 2.00 | 15.0 |
| Lime oil expressed | 0.60 | 0.090 | 0.70 | 12.9 |
| Sum | 72.9 — passes |
Now raise the bergamot to 2.00% of the concentrate: 0.300% in the product, 75.0% of its limit. Bergamot alone is still under its limit, but the sum is 75.0 + 15.0 + 12.9 = 102.9 — the formula fails. Options: reduce one of the oils, replace part of the bergamot with a furocoumarin-free grade, or lower the concentrate in the product.
(Rounded to one decimal; 0.090 ÷ 0.70 = 12.86%.)
Unknown furocoumarin content and FCF grades
- IFRA's guidance says that if the furocoumarin level is unknown, the restriction for the specific natural in the citrus Standard applies — so an expressed oil with no data is counted at its full limit.
- Furocoumarin-free ("FCF") or bergapten-reduced grades are sold with a stated content. How such a grade counts depends on that content and on the Standard's wording; keep the supplier's certificate and the grade on the material record (SDS and specifications).
- Purchased compounds may contain these oils without telling you. The supplier's IFRA certificate for your category covers them; a compound plus your own citrus oils still needs the combination checked by someone who knows both — ask the supplier for its contribution.
In practice
- Record the grade (expressed, distilled, FCF) on every citrus material.
- Keep a list of which materials in your library belong to the combination group.
- For each leave-on product, compute the sum at the product's concentration, and keep it with the formula version.
- Re-check when the concentration, the category or the grade changes.
RUŌOD Lab flags a row whose relative percentage exceeds the limit you recorded on that material. It checks materials one at a time; the combination sum is a separate calculation to keep with the formula. More on the derivation of IFRA limits is in IFRA QRA explained, and leave-on products where this matters most are covered in beard oil fragrance and fragrance in lotion.
Sources
- IFRA — Guidance for the use of the IFRA Standards (51st Amendment, June 30, 2023), § 1.6.1 (Tables 2–5) and § 1.6.1.2 (policy on furocoumarins, combination rule); checked October 11, 2026.
- IFRA — IFRA Standards (the current limits).
Frequently asked questions
Does the combination rule apply to a candle with bergamot oil?
No. Category 12 products have no skin contact, and IFRA's guidance says phototoxicity considerations do not apply to them.
Does methyl N-methyl anthranilate count in the sum?
No. The combination rule covers only the furocoumarin-containing naturals. Materials that are phototoxic in themselves are each checked against their own Standard.
Is distilled lime oil phototoxic?
Distillation leaves most furocoumarins behind, so distilled lime is generally not restricted the way expressed lime is. Check the grade's documentation and the Standard's wording for the oil you buy.
Written and reviewed by the RUŌOD Lab team. This article is general education about perfume formulation and record-keeping; it is not legal, regulatory or safety advice, and the examples are illustrations, not validated commercial formulas. How we write and check these guides.