The hazard score on Skin Deep is calculated in steps.
We categorize the studies and data contained in Skin Deep into 17 general hazard categories: cancer, reproductive/developmental toxicity, neurotoxicity, endocrine disruption potential, allergies/immunotoxicity, restrictions/warnings, organ system toxicity, persistence/bioaccumulation, multiple/additive exposure, mutations, cellular/biochemical changes, ecotoxicity, occupational hazards, irritation, absorption, impurities, and miscellaneous.
We then assign each study/data source a score between 0 and 100 based on the weight of evidence. For example, a "known human carcinogen" is assigned a 100 for the cancer category while a "probable human carcinogen" is given a much lower score (55). The breakdown for each category may be found in tables below.
Next, we calculate overall ingredient scores in each of the 17 categories:
- For restrictions/warnings, multiple/additive exposure, impurities, and miscellaneous, we simply add up all the scores assigned in step 2. This means that the "restrictions/warnings" score for a chemical banned in Europe & Japan will be higher than for a chemical only banned in Europe.
- For the remaining categories, we apply the highest score found to that category for that ingredient. This means that if a chemical was determined to be a "known human carcinogen" by EPA and a "probable human carcinogen" by the EU, it will only receive the score for being a "known human carcinogen".
Next, we weight each category score (except absorption) and take the sum of the weighted factors as the raw hazard score. The weighting factors are listed in a table below.
We then weight the raw hazard score by the absorption category score. The absorption category score takes into account the particle size and the ability of an ingredient to enhance penetration.
Products
We return to the 17 categories to calculate a product score. For each category (except absorption), we add the highest scoring ingredient to the average score for the rest of the ingredients. For example, if a product contained water, coal tar, and sodium chlorite, the cancer score would be 100 (from the known carcinogen score for coal tar) + 15 (from the average of water [0] and sodium chorite [30 - limited evidence]). The resulting raw cancer score would be 115.
Just as with an ingredient, these category scores (except absorption) are weighted and then summed to produce a raw score. The weighting factors are listed in a table below.
We then weight the raw product score by the absorption category score. The absorption weighting factor includes an assessment of penetration enhancers, and nano-scale ingredients.
Final scaling of hazard scores
In the final step for deriving product and ingredient hazard scores, all scores are scaled from 1 to 10, with 10 corresponding to ingredients and products with the greatest concern, and 1 to ingredients and products with the least concern. We assign a score of 10 to the top 5% most hazardous products and ingredients, and then scale down uniformly to 1 for scores lower than this.
Major categories of concern and their weighting factors
We categorized every piece of toxicity and hazard information in our integrated database into one of 17 categories. We developed these categories based on our review of available data, and modeled them after a variety of toxicity classification systems developed by government, industry, and academic organizations. We assigned to each of these categories a weighting factor representing a judgment on their relative importance to and impact on human health. We assigned higher weighting factors to categories of health concern for which studies provide evidence for effects at low doses, for permanent effects stemming from exposures during development, for toxicity endpoints that tend to impact multiple biological systems in the body or to impair reproduction. These endpoints include cancer, reproductive and development effects, immunotoxicity, neurotoxicity, and effects stemming from exposures to endocrine (hormone) disruptors. Organ systems that are more localized, such as gastrointestinal, kidney, respiratory, etc. are weighted in the mid-range. Toxic endpoints that measure adverse effects at the cellular level, which may or may not have implications for human health (such as mutations or biochemical changes) are weighted the least. This scoring system does not account for individual sensitivities or differences between the severities of different health endpoints within a particular category.
Table 1: Hazard categories and weighting factors
| Category | Weighting factor | Description |
|---|---|---|
| Cancer | 1.0 | linked to cancer in government, industry, or academic studies or assessments. |
| Developmental/reproductive toxicity | 1.0 | linked to developmental and reproductive toxicity, a broad class of health effects that can range from infertility and reproductive organ cancers to birth defects and developmental delays for children. |
| Endocrine disruption | 1.0 | the body's natural hormones, the chemicals that carry messages across the body to manage growth, tissue repair, and reproduction. |
| Allergies/immunotoxicity | 1.0 | linked to immunotoxicity, or harm to the immune system, a class of health problems that manifest as allergic reactions or an impaired capacity to fight disease and repair damaged tissues in the body. |
| Miscellaneous | 1.0 | Includes toxicity endpoints that didn't fit in another category, efficacy scores (scores that might counteract toxicity scores), and scores for unidentified ingredients. |
| Neurotoxicity | 1.0 | linked to neurotoxicity, or harm to the brain and nervous system, a class of health problems that can range from subtle developmental delays to chronic nerve degeneration diseases. |
| Use restrictions | 0.9 | prohibited for use in cosmetics, or subject to concentration, use, or manufacturing method restrictions, according to industry safety guidelines and government requirements and guidance from the U.S., E.U., Japan, and Canada. |
| Organ system toxicity (non-reproductive) | 0.5 | linked to toxicity of one or more biological systems in the body (cardiovascular, stomach and digestive trace, respiratory system, etc.) through laboratory studies or studies of people. |
| Biochemical or cellular level changes | 0.3 | the ability to affect the body at a cellular or biochemical level that may have larger, but poorly understood health implications. |
| Multiple, additive exposure sources | 0.3 | also found as contaminants in tap water and food, as ingredients in other kinds of consumer products, or in people in biomonitoring studies that measure chemicals in blood, urine, and other fluids and tissues. |
| Mutations | 0.3 | linked to both cancer and developmental defects. Includes government, industry, or academic assays, studies and assessments. |
| Persistence and bioaccumulation | 0.3 | persistent and/or bioaccumulative, resisting normal chemical breakdown in the environment; building up in wildlife, the food chain, and people; and lingering in body tissues for years or even decades after exposure. |
| Ecotoxicology | 0.2 | linked to toxicity of wildlife that may include fish, wildlife, plants, or other wild organisms. |
| Occupational hazards | 0.2 | linked to hazards for workers exposed on the job, including acute dangers from chemical handling, or longer term health effects from routine occupational exposures. |
| Irritation (skin, eyes, or lungs) | 0.1 | linked to irritation of the skin, eyes, or lungs according to government assessments, industry reviews, and peer-reviewed studies. |
| Enhanced skin absorption | 0.0 | an enhanced capacity to absorb through this skin by virtue of chemical properties like penetration enhancing abilities or small particle size (including nanoparticles), or by virtue of where it is applied on the body (on infant skin, lips, or damaged skin). |
| Decreased skin absorption | 0.0 | an decreased capacity to absorb through this skin by virtue of chemical properties like penetration enhancing abilities or large particle size (including nanoparticles), or by virtue of where it is applied on the body (on infant skin, lips, or damaged skin). |
| Data gaps | 0.0 | linked to data gaps that constitute the absence of basic toxicity studies and hazard and safety assessments in Skin Deep's core databases, or that reflect findings of data deficiencies in government or industry assessments. |
| Contamination concerns | 0.1 for ingredients 0.01 for products | may be contaminated with toxic impurities, many of which are linked to cancer, according to government and cosmetic industry ingredient safety assessments or peer-reviewed studies. |
We assigned numeric hazard scores for each scoring category based on professional judgment of the relative importance of each with respect to potential health concerns. These scores were informed by a number of factors, including the weight of the evidence associated with each scoring category (e.g. whether the chemical categorization is derived from a full government assessment or from a single peer-reviewed study), and by other hazard classification systems, such as the Nordic Substances Database.
For most types of hazards, we assign scores as a function of the lowest known harmful dose where that information is available, the weight of the evidence (limited, moderate, and strong evidence), and the source of the data (individual study; literature review, industry review panel, or major government study; and comprehensive government assessment). We use the scores shown below in our calculations of final hazard (concern) scores for ingredients and products, as described in subsequent sections. The tables below detail the hazard scoring system.
Table 2: Hazard scoring framework for cancer, developmental and reproductive toxicity, endocrine disruption, immunotoxicity, and multiple organ system toxicity
The scores we assign for these hazard categories range from a maximum of 100 for chemicals known to be toxic to humans in a given category as determined by a definitive government assessment, to 20 for chemicals showing limited evidence for toxicity in a non-academic review, down to 0 for chemicals determined not likely to be human toxicants.
| Hazard score category | Data source | Hazard Score |
|---|---|---|
| Known human toxicant | Government assessment | 100 |
| Possible human toxicant | Government assessment | 55 |
| Limited evidence of human toxicity | Government assessment | 30 |
| Strong evidence for human toxicity | Literature review, industrial panel, or major government study | 55 |
| Moderate evidence for human toxicity | Literature review, industrial panel, or major government study | 30 |
| Limited evidence for human toxicity | Literature review, industrial panel, or major government study | 20 |
| One or more animal studies show effects at very low doses | Individual scientific or peer-reviewed study | 30 |
| One or more animal studies show effects at low doses | Individual scientific or peer-reviewed study | 20 |
| One or more animal studies show effects at moderate doses | Individual scientific or peer-reviewed study | 10 |
| One or more animal studies show effects at high doses | Individual scientific or peer-reviewed study | 5 |
| Not likely to be a human toxicant | Government assessment, literature review, industrial panel, or major government study | 0 |
Table 3: Hazard scoring framework: mutations
We assign scores for mutation data essentially the same as for other hazard classifications (as in Table 2), but make modifications to account for the unique range of tests available to define mutation, as shown in this table. Scores we assign for mutation range from 100 for a known mutagen as determined by a definitive government assessment, to 10 for ingredients for which one or more studies on micro-organisms show positive mutation results, to 0 for ingredients determined not likely to be mutagens in humans based on a definitive government review.
| Hazard score category | Data source | Hazard Score |
|---|---|---|
| Known mutagen | Government assessment | 100 |
| Possible mutagen | Government assessment | 55 |
| Strong evidence for mutagenity in human cells | Literature review, industrial panel, or major government study | 55 |
| Moderate evidence for mutagenity in human cells | Literature review, industrial panel, or major government study | 30 |
| Limited evidence of mutagenity in human cells | Government assessment | 30 |
| One or more studies on mammalian cells show positive mutation results | Individual scientific or peer-reviewed study | 30 |
| Limited evidence of mutagenity in human cells | Literature review, industrial panel, or major government study | 20 |
| One or more studies on non-mammalian cells show positive mutation results | Individual scientific or peer-reviewed study | 20 |
| One or more studies on micro-organisms show positive mutation results | Individual scientific or peer-reviewed study | 10 |
| Not likely to be a mutagen | Government assessment, literature review, industrial panel, or major government study | 0 |
Table 4: Hazard scoring framework: biochemical and cellular level changes
We assign scores for biochemical and cellular level changes, where the human health impact may be unclear. The framework is essentially the same as for other hazard classifications (as in Table 2) with some modifications to account for the unique range of tests available to define biochemical changes and because more significant reviews generally are undertaken only on concrete human health effects. Scores we assign for biochemical and cellular level changes range from 100 for a reactive oxygen species that are beginning to be linked up to definitive health effects to 5 for ingredients for high-dose studies showing biochemical changes.
| Hazard score category | Data source | Hazard Score |
|---|---|---|
| Produces excess reactive oxygen species that can interfere with cellular signaling, cause mutations, lead to cell death and may be implicated in cardiovascular disease. | Individual scientific or peer-reviewed study | 100 |
| Interferes with gene expresion | Individual scientific or peer-reviewed study | 30 |
| One or more animal studies show effects at very low doses where the human health implications are not yet well understood | Individual scientific or peer-reviewed study | 30 |
| One or more animal studies show effects at low doses where the human health implications are not yet well understood | Individual scientific or peer-reviewed study | 20 |
| One or more animal studies show effects at moderate doses where the human health implications are not yet well understood | Individual scientific or peer-reviewed study | 10 |
| One or more animal studies show effects at high doses where the human health implications are not yet well understood | Individual scientific or peer-reviewed study | 5 |
Table 5: Hazard scoring framework: Assigning categories based on the Nordic Substances Database hazard potency framework
A scoring framework implemented in the 2007 update of Skin Deep accounts for detailed toxicity study findings. These findings are reviewed by EWG staff, and are drawn from the open scientific literature and from a government database containing over 6000 peer-reviewed references.
We assign hazard scores to each recorded lowest toxic dose according to weighting factors used in the Nordic Substances Database classification system, as shown in Table 5. No attempt was made to evaluate the length of time or dosing regimen (such as differentiating between chronic and sub-chronic studies) for repeat doses or accounting for route of exposure. In cases of acute studies where the LOEL (Lowest Observed Effect Level) instead of the LD50 (Lowest Dose producing 50% mortality of test animals) was reported, the doses were multiplied by a factor of 10 to estimate the LD50.
| Potency | Acute Studies1 (LD50 - mg/kg of body mass) | Repeat Dose Studies2 (LOAEL - mg/kg day of body mass) |
|---|---|---|
| Very highly toxic - very low dose | <25 | <2.5 |
| Highly toxic - low dose | 25<=Dose<200 | 2.5<=Dose<20 |
| Moderately toxic - moderate dose | 200<=Dose<2000 | 20<=Dose<200 |
| Low toxicity - high dose | Dose>=2000 | Dose>=200 |
- 1. LD50 refers to the chemical dose at which 50% of the animals died.
- 2. LOAEL is the Lowest Observed Adverse Effect Level which is the lowest dose of a chemical at which a harmful effect is observed in a lab animal.
Table 6: Hazard score framework: Occupational hazards
| Potency | Occupational 8 hr TLVs and PELs (mg/m3) |
|---|---|
| Very highly toxic - very low dose | <3.47 |
| Highly toxic - low dose | 3.47<=Dose<27.9 |
| Moderately toxic - moderate dose | 27.9<=Dose<279 |
| Low toxicity - High dose | >=279 |
Note: We derived the occupations exposure factors shown above by converting the animal study doses define potency in the Nordic Substances Database (see Table 6) into equivalent concentrations in workplace air assuming a 70 kg male, 15 breathes/minute, 0.7 liters/breathe over an 8-hour workday.
Table 7: Hazard score framework: Government or industry restrictions or guidelines
Scores in this category range from a maximum of 100 for a violation of a ban to 1 for caustic chemicals used as a pH balancer in a specific product.
| Finding | Data source | Hazard Score |
|---|---|---|
| Banned or found unsafe for use in cosmetics | Government assessment | 100 |
| Violations of restrictions and safety warnings | Government assessment | 90 |
| Not safe in cosmetics for specific use | Literature review, industrial panel, or major government study | 40 |
| Safe use with an industry determined concentration limit | Literature review, industrial panel, or major government study | 25 |
| Safe use with specific consumer instructions | Literature review, industrial panel, or major government study | 10 |
| Safe use as a pH adjuster | Literature review, industrial panel, or major government study | 1 |
| Approved for use | Government assessment, literature review, industrial panel, or major government study | 0 |
Table 8: Hazard score framework: persistence and bioaccumulation
Many chemicals persist in the environment and bioaccumulate in people and the environment. EWG has compiled listings of persistent, bioaccumulative compounds from authoritative bodies, for compounds considered potentially hazardous to humans or the environment.
For the hazard score category titled "Ingredients not fully identified," we assign a score of 100, flagging ingredients with unknown identity, such as fragrance and unidentified essential oils.
| Finding | Level of finding | Hazard Score |
|---|---|---|
| Persistent, bioaccumulative in wildlife and humans | Government assessment | 100 |
| Persistent, bioaccumulative in wildlife | Government assessment | 50 |
Table 9: Hazard score framework: multiple exposure routes
| Finding | Level of finding | Hazard Score |
|---|---|---|
| Used in food or as an additive with limited or no toxicity information available | Government assessment | 100 |
| Contaminant in tap water | Government assessment | 100 |
| In other consumer products besides personal care products | Government assessment | 50 |
| High production volume chemical | Government assessment | 50 |
| Environmental releases by industry | Government assessment | 50 |
| Used as an inert ingredient in pesticides | Government assessment | 50 |
| Designated as safe for use in food | Government assessment | 0 |
Adjusting hazard scores for skin absorption potential
In the penultimate step for deriving product and ingredient hazard scores, we adjust preliminary scores to account for increased potential for an ingredient to penetrate the skin. We account for the potential enhanced absorption of a product stemming from the presence of penetration enhancing ingredients, and known or potential nano-scale ingredients (NanoWerk 2007).
For nano-scale and potentially nano-scale ingredients, the ingredient scores are scaled as in Equation 3 with scaling factors of 1.5 and 1.25, respectively. The overall product scores are not adjusted. In cases where the skin absorption potential is lowered, we also scale downwards for the individual ingredients. Scores are multiplied for 0.5 for reduced or limited absorption, and 0.25 where the ingredient has been shown not to absorb into intact skin. Only for ingredients shown not to absorb into intact, damaged, infant, and thinner skin, is the factor reduced to 0.
Skin Deep's Health Concern Summary Bars
Hazard scores are reflected as bars at the top of each ingredient, product, brand, and company page. These bars represent the relative hazard rating for that ingredient or ingredient list. Using the general hazard category scores described above, the bars are filled in from left to right with a score of 0 on the left and the maximum on the right (described below). Each page in the Skin Deep online database includes a bar for overall hazard; cancer; developmental/reproductive toxicity; allergies/immunotoxicity; and use restrictions.
Ingredient Pages
The maximum value for each bar is 100. For example, a "known human carcinogen" is assigned a 100 for the cancer category while a "probable human carcinogen" is given a much lower score (55). (See more about the scoring above.) Other concerns are separated into three categories:
- "strong" - category score>60; the bar is 100% full
- "moderate" - category score>10; the bar is 66% full
- "lesser" - category score>0; the bar is 33% full
Product Pages
The calculation of category scores is the sum of the maximum value for its ingredients + the average of the other ingredients. For "cancer" and "developmental/reproductive toxicity", the bars are scaled from 0 to 100. For "use restrictions" and "allergies/immunotoxicity", the bars are scaled from 0 to 150. Other concerns are listed only if the score is >15. The bar is then scaled based on the number of other concerns that are listed with a scale from 0 to 15 possible extra concerns.
Company and Brand Pages
Hazard category scores for companies and brands are taken as the average value for ingredients used by the brand/company. Category bars displayed in Skin Deep are scaled from 0 to 100. Other concerns are listed only if the average score is >15. The bar is scaled based on the number of other concerns that are listed, with a scale from 0 to 15 possible extra concerns.
