Home Toxicity Score: Methodology

The scoring formula

Each of the 13 quiz questions returns a per-question score from 0 to 10, where higher means lower exposure. Per-question scores are multiplied by their category weight, summed, divided by the total weight that was actually answered, and scaled to 100. The result is rounded to the nearest integer and mapped to a letter grade.

finalScore = round( sum(perQuestion * weight) / sum(weight) * 10 )
grade = A >= 80, B >= 60, C >= 40, D >= 20, F < 20

Weights were calibrated by approximate daily exposure magnitude per category. Water filtration carries the heaviest weight because tap water is the largest single daily ingestion pathway for PFAS, lead, and disinfection byproducts in the United States. Indoor air categories (gas combustion, HVAC, fragrance) collectively carry the second-largest weight because adults spend roughly 90% of their time indoors. Lawn pesticides carry a smaller weight because the dominant indoor route is shoe-tracked residue, which is mostly avoidable with a shoes-off household policy.

Category weights (sum to 1.00)

Category	Weight
Cookware	9%
Food Storage	7%
Water Filtration	13%
Cleaning Products	10%
Mattress	8%
Air Quality (Fragrance)	7%
Personal Care	8%
Children's Products	6%
Home Age & Materials	5%
Indoor Combustion	8%
HVAC / Air Filtration	6%
Lawn & Garden Chemicals	5%
Recent Swaps	8%

Per-question scoring rationale

1. 1. What type of cookware do you primarily use?

   PTFE/PFOA-coated nonstick can release particulate fumes when overheated above 500°F [EPA assessment]; cast iron and stainless steel have no comparable exposure pathway.

   • Teflon/nonstick (PTFE) scores 1/10
   • Ceramic-coated scores 6/10
   • Cast iron / stainless steel scores 10/10
   • Mostly safe with some nonstick scores 5/10

2. 2. How do you store leftover food?

   BPA, BPS, and ortho-phthalates can migrate from plastic into food, especially when heated [human biomonitoring]. Glass and stainless eliminate this pathway.

   • Plastic containers scores 2/10
   • Glass or stainless steel scores 10/10
   • Mix of plastic and glass scores 5/10
   • Mostly Ziplock / single-use plastic bags scores 1/10

3. 3. Do you filter your drinking water?

   EPA and EWG tap-water testing has detected PFAS, lead, chlorine byproducts, and arsenic in many US municipal supplies [regulatory monitoring]. Filter quality varies dramatically.

   • No filter scores 0/10
   • Brita / basic carbon pitcher scores 4/10
   • Reverse osmosis or NSF/ANSI 53+58 certified scores 10/10
   • Don't know what I have scores 2/10

4. 4. What cleaning products do you use?

   Conventional cleaners can emit VOCs and contain quaternary ammonium compounds linked to respiratory effects [occupational epidemiology]. EPA Safer Choice and MADE SAFE products use vetted ingredient lists.

   • Conventional brands (Lysol, Clorox) scores 1/10
   • "Green" brands (Method, Seventh Generation) scores 5/10
   • Certified non-toxic (Branch Basics, MADE SAFE) scores 9/10
   • DIY / vinegar-based scores 8/10

5. 5. What's your mattress situation?

   Polyurethane foam mattresses can off-gas VOCs (formaldehyde, toluene) for months; flame retardants are now mostly halogen-free but disclosure varies [chamber emissions testing]. Off-gassing typically declines after the first year.

   • Conventional, under 5 years old scores 3/10
   • Conventional, over 5 years old (mostly off-gassed) scores 6/10
   • GOTS or GOLS certified organic scores 10/10
   • Memory foam (CertiPUR-US or similar) scores 4/10

6. 6. Do you use air fresheners or scented candles?

   Plug-ins and paraffin candles can emit phthalates and combustion byproducts in poorly ventilated rooms [chamber studies]. Essential oils are not risk-free but emit less; opening windows is the biggest single intervention.

   • Plug-in air fresheners scores 0/10
   • Scented candles regularly (paraffin) scores 2/10
   • Essential oil diffuser only scores 6/10
   • None / open windows scores 10/10

7. 7. What personal care products do you use?

   Shampoo, lotion, and deodorant can contain parabens, phthalates, and PFAS that absorb dermally; biomonitoring shows daily users carry detectable levels [human biomonitoring]. EWG VERIFIED and MADE SAFE programs screen these out.

   • Conventional drugstore brands scores 1/10
   • "Clean" brands but not certified scores 5/10
   • EWG VERIFIED or MADE SAFE certified scores 10/10
   • Minimal / fragrance-free scores 8/10

8. 8. Do you have children under 12?

   Children have higher exposure per body weight and developing endocrine systems [Landrigan, NIEHS]. Choices that matter most: bottles, pacifiers, sleep environment, and floor-level products.

   • Yes - using conventional baby/kids products scores 1/10
   • Yes - using certified non-toxic baby/kids products scores 8/10
   • No children at home scores 10/10

9. 9. How old is your home?

   Homes built before 1978 may contain lead-based paint or asbestos in older flooring/insulation [HUD/EPA]. Pre-2010 homes are more likely to have legacy formaldehyde in pressed-wood cabinets.

   • Built before 1980 scores 2/10
   • Built 1980-2000 scores 5/10
   • Built 2000-2015 scores 7/10
   • Built after 2015 scores 9/10

10. 10. Do you cook on a gas stove?

    Gas stoves emit nitrogen dioxide (NO₂) and benzene during use; childhood asthma risk is elevated in homes with gas cooking [Gruenwald 2023, IJERPH meta-analysis]. Hood ventilation reduces exposure substantially.

    • Yes, gas stove without range hood ventilation scores 1/10
    • Yes, gas stove with range hood vented outside scores 5/10
    • Electric or induction scores 10/10
    • I rarely cook at home scores 7/10

11. 11. How often do you change your HVAC / air filter?

    A clogged or low-MERV filter lets PM2.5, allergens, and VOCs recirculate. EPA recommends MERV 13+ for indoor air quality and changes every 1-3 months in normal homes.

    • Never / I forget scores 1/10
    • Once a year or less scores 3/10
    • Every 3 months with MERV 11+ scores 8/10
    • Monthly / MERV 13+ or HEPA scores 10/10

12. 12. Do you use synthetic lawn or garden pesticides?

    Glyphosate, 2,4-D, and pyrethroid residues can track indoors on shoes and pets [EPA dust monitoring]. Removing shoes at the door and switching to OMRI-listed products reduces residue meaningfully.

    • Yes, regularly (Roundup, Scotts, etc.) scores 1/10
    • Occasionally / spot treatments scores 4/10
    • Organic or OMRI-listed only scores 9/10
    • No yard / no use scores 10/10

13. 13. Have you replaced any of these recently with non-toxic versions?

    Select all that apply.

    • PVC-free shower curtain scores 2/10
    • Removed dryer sheets / fabric softener scores 2/10
    • Switched laundry detergent (fragrance-free or certified) scores 2/10
    • Removed shoes at the door (reduces tracked-in pesticides) scores 2/10
    • Added a HEPA air purifier in bedroom scores 2/10
    • None of these scores 0/10

Source data

• EPA Safer Choice ingredient screening
• NSF/ANSI 53 and NSF/ANSI 58 drinking water standards
• EWG Tap Water Database contaminant levels
• EWG Skin Deep personal care ingredient hazard ratings
• MADE SAFE certified product registry
• Global Organic Textile Standard (GOTS) for textiles and mattresses
• Global Organic Latex Standard (GOLS) for natural latex
• EPA Indoor Air Quality guidance on PM2.5, NO2, VOCs
• CDC Biomonitoring for human exposure baselines (BPA, phthalates, PFAS)

Grade thresholds

Grade	Score range	Label
A	80-100	Low Toxicity
B	60-79	Moderate
C	40-59	Elevated Exposure
D	20-39	High Exposure
F	0-19	Very High Exposure

Limitations

The Home Toxicity Score is a directional triage tool, not a clinical exposure measurement. It cannot account for individual factors like body weight, metabolic rate, pregnancy, occupational exposure, or local water quality variation. The scoring system is built on hazard-weighted exposure averages, not personalized risk modeling.

Where evidence of harm is uncertain or contested in the literature, we use conservative scoring (favoring the lower-exposure option) but never present hazard as confirmed risk. Study type labels in the question subtitles ([animal study], [human biomonitoring], [regulatory monitoring], etc.) reflect the strength of the underlying evidence.

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