The evidence
Each criterion with what we found, where we found it and when. Anything we could not confirm says so.
NTH criteria
NTH Framework v1.2. Score 38.4 (raw 29.0 of 100), calibrated so the best hotel in this edition (Santa Monica Proper Hotel) reads 90. Evidence retrieved 2026-10-22.
Sleep3.0 / 24
The room as an instrument for deep, uninterrupted, circadian-aligned rest.
Mattress & sleep system
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 5 pts
Unknown
Bedding & textiles
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 4 pts
Unknown
Sleep programme & pillow menu
Hotel-reported · in the best room
Sleep programme with tracker, consultation, yoga nidra; pillow menu.
Blackout
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Circadian & warm evening lighting
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
In-room red light
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Acoustic quiet
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 4 pts
Unknown
EMF & Wi-Fi-off options
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Air0.0 / 12
What you breathe for eight hours a night: filtered, fresh, smoke-free and unperfumed.
In-room purification
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 5 pts
Unknown
Ventilation & building standard
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 3 pts
Unknown
Smoke-free policy
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Fragrance-free & low-allergen rooms
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Water0.0 / 12
Clean water to drink, and to shower and bathe in.
Filtered drinking water
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 5 pts
Unknown
Shower & bath filtration
Not yet reviewed · in the best room
Unknown. We have asked the hotel.
0.0 / 5 pts
Unknown
Gentler pool & hydrotherapy water
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Nourishment4.0 / 10
Food and drink that heal rather than merely please.
Organic & local sourcing
Hotel-reported · across the property
Produce from its own kitchen gardens; seasonal.
Clean-ingredient standard
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 3 pts
Unknown
Clean minibar & in-room hydration
Hotel-reported · in the best room
Reusable glass bottles replace plastic.
Nutrition guidance
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 1 pts
Unknown
Movement7.0 / 10
The means to train, stretch and move, indoors and out.
Gym completeness
Hotel-reported · across the property
Gym.
Classes & studios
Hotel-reported · across the property
Hatha yoga classes, yoga pavilion, on-demand classes.
Swimming
Hotel-reported · across the property
Indoor pool.
Outdoor activity
Hotel-reported · across the property
Forest bathing.
Holistic Wellness9.0 / 19
Healing traditions and the recovery technology that complements them.
Spa facility
Hotel-reported · across the property
Ten treatment rooms; Vitality Suite with sauna, steam, laconium.
Traditional & integrative modalities
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 4 pts
Unknown
Mind & breath
Hotel-reported · across the property
Yoga nidra, meditation, pranayama, underwater sound therapy.
Heat therapy
Hotel-reported · across the property
Infrared sauna, herbal sauna.
Cold therapy
Hotel-reported · across the property
Cryotherapy.
Photobiomodulation & PEMF
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Clinical longevity (IV, HBOT, diagnostics)
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 4 pts
Unknown
Materials & Setting6.0 / 13
What touches the skin and surrounds the stay: finishes, products, cleaning, and the landscape beyond the door.
Natural, low-VOC finishes
Hotel-reported · in the best room
Rooms blend natural materials and Portuguese design.
Clean bath & body amenities
Hotel-reported · in the best room
Sustainable bathroom amenities.
Non-toxic spa & nail products
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Non-toxic housekeeping & plastic-free operations
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Green & blue space
Hotel-reported · across the property
Historic gardens, community forest and an adopted riverbank.
Walkability & low-impact mobility
Not yet reviewed · across the property
Unknown. We have asked the hotel.
0.0 / 2 pts
Unknown
Our review
At a glance
- Fragrance
- 5 not yet reviewed
- Air
- 5 not yet reviewed
- Cleaning & care
- 4 not yet reviewed
- Sleep & materials
- 5 not yet reviewed
- Water & pools
- 4 not yet reviewed
- Food
- 1 hotel-reported, 1 not yet reviewed
- Light & quiet
- 2 not yet reviewed
- Building
- 3 not yet reviewed
Nothing reviewed yet: every criterion is shown as not yet reviewed.
Nothing reviewed yet25 of 25 not yet reviewed
Counts cover the 25 scored criteria; the other 5 windows are context.
Checked
Read the full profileThe ledger
Fragrance
Added scent is the most common complaint from sensitive guests, and the hardest thing to see on a booking page.
No added fragrance in rooms
Not yet reviewed.
No scent marketing
Not yet reviewed.
Fragrance-free laundry
Not yet reviewed.
Unscented bath products
Not yet reviewed.
Unscented spa options
Not yet reviewed.
So far, the hotel says: The spa lists ten treatment rooms and a Vitality Suite with a sauna, infrared sauna, steam room, laconium and herbal sauna.
Our note. Whether treatments can be given without essential oils, or the herbal sauna without scent, is not stated.
How we know
What we look for. Treatments, saunas and steam rooms available without essential oils or scent infusions.
Why it matters. Essential oils are fragrance: the EU’s scientific committee lists several natural extracts, as well as single fragrance chemicals, among established contact allergens. A shared sauna with a scent infusion is hard to avoid.
Source: EU Scientific Committee on Consumer Safety, Opinion on fragrance allergens in cosmetic products ()
Source 1: Hotel website: wellness and spaUndated · read 22 Oct 2026
Know something about fragrance here that we don’t? Tell us
Air
What you breathe for eight hours a night: smoke history, fresh air, filtration and anything burning in the room.
Smoke-free property
Not yet reviewed.
Opening windows
Not yet reviewed.
Filtered fresh air
Not yet reviewed.
In-room air purifier
Not yet reviewed.
No in-room combustion
Not yet reviewed.
Know something about air here that we don’t? Tell us
Cleaning & care
How a room is cleaned, treated and prepared, and whether a request for a gentler clean is actually honored.
Low-chemical housekeeping
Not yet reviewed.
No ozone or biocide treatments
Not yet reviewed.
Low-chemical pest control
Not yet reviewed.
Sensitive-guest preparation
Not yet reviewed.
Know something about cleaning & care here that we don’t? Tell us
Sleep & materials
The textiles, mattress and floor you spend the night closest to, and how allergen-aware the room is.
Tested or organic bed linen
Not yet reviewed.
So far, the hotel says: The accommodation page mentions organic cotton sheets.
Our note. No textile certification is named.
How we know
What we look for. Sheets and towels certified to a residue-testing standard such as OEKO-TEX Standard 100, or certified organic.
Why it matters. Certifications such as OEKO-TEX Standard 100 test the finished fabric, down to the thread, against a list of restricted substances, which lowers skin exposure over a night’s sleep.
Source: OEKO-TEX, OEKO-TEX Standard 100 (undated)
Source 2: Hotel website: accommodationUndated · read 22 Oct 2026
Mattress materials disclosed
Not yet reviewed.
So far, the hotel says: The accommodation page says the Sleep With Six Senses programme brings handmade mattresses and temperature-regulating pillows and duvets.
Our note. The mattress maker and materials are not named.
How we know
What we look for. The hotel says what its mattresses are made of and how flame-retardancy is achieved.
Why it matters. Flame retardants have been added to mattresses and seating foam, and the US National Institute of Environmental Health Sciences lists possible effects including endocrine and thyroid disruption. How much a mattress adds to anyone’s exposure is still debated; disclosure lets guests choose.
Source: US National Institute of Environmental Health Sciences, Flame retardants (undated)
Source 2: Hotel website: accommodationUndated · read 22 Oct 2026
Hard floors
Not yet reviewed.
Allergy-friendly rooms
Not yet reviewed.
Pet-free rooms
Not yet reviewed.
So far, the hotel says: Small pets under seven kilograms are allowed at the resort.
Our note. Whether some rooms are kept pet-free is not stated.
How we know
What we look for. Rooms or floors where animals are never allowed, cleaned to a separate routine.
Why it matters. Pet allergen can stay on carpets and furniture for months and travels on clothing. For allergic guests a room animals never enter matters more than any amenity.
Source: US National Institute of Environmental Health Sciences, Pet allergens (undated)
Source 2: Hotel website: accommodationUndated · read 22 Oct 2026
Know something about sleep & materials here that we don’t? Tell us
Water & pools
Drinking water, shower water and pool air.
Filtered or tested drinking water
Not yet reviewed.
Water safety plan
Not yet reviewed.
Shower filters
Not yet reviewed.
Shown for information; not scored.
Outdoor or low-chloramine pools
Not yet reviewed.
So far, the hotel says: The spa has a heated indoor pool with underwater sound therapy and massage jets, and a vitality pool.
Our note. The page does not describe the pool’s ventilation or how its water is treated.
Shown for information; not scored.
How we know
What we look for. Pools are outdoors, or indoor pools have dedicated ventilation and monitored combined chlorine.
Why it matters. Chloramines irritate the skin, eyes and airways, and they build up in the air of indoor pools without enough ventilation. Outdoor pools, and good ventilation for indoor ones, keep levels low.
Source: US CDC, Chloramines and pool operation ()
Source 1: Hotel website: wellness and spaUndated · read 22 Oct 2026
Context, not scored: almost every pool in this catalog is outdoors, so it says little about one hotel against another.
Know something about water & pools here that we don’t? Tell us
Food
Allergen care first; where the produce comes from second.
Allergen-aware kitchen
Not yet reviewed.
Garden or organic produce
Hotel-reportedacross the property
The hotel says: The resort says it grows vegetables, fruit and herbs in its own garden and serves homegrown produce in its restaurants.
Our note. Whether the gardens are farmed organically is not stated.
Shown for information; not scored.
How we know
What we look for. A meaningful share of the kitchen’s produce is grown on site or certified organic.
Why it matters. A large review found detectable pesticide residues about four times as often in conventional crops as in organic ones. Over a short stay the difference in exposure is small, so we show this as a note on the kitchen, not a scored health factor.
Source: Barański et al., British Journal of Nutrition, Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses ()
Source 3: Hotel website: sustainabilityUndated · read 22 Oct 2026
Kitchen note, not scored.
Know something about food here that we don’t? Tell us
Light & quiet
Darkness and silence at night, and radio-quiet options for guests who want them.
Darkness and quiet
Not yet reviewed.
So far, the hotel says: The spa offers a sleep programme that combines sleep-tracker data with a consultation, yoga nidra and meditation.
Our note. Blackout shades and sound insulation in the rooms are not described.
How we know
What we look for. Blackout shades and sound insulation that let the room become properly dark and quiet.
Why it matters. Night-time noise fragments sleep; the WHO’s night noise guidelines set a target of 40 dB outside the bedroom. A dark, quiet room is the simplest sleep aid there is.
Source: WHO Regional Office for Europe, Night noise guidelines for Europe ()
Source 1: Hotel website: wellness and spaUndated · read 22 Oct 2026
Radio-quiet options
Not yet reviewed.
Shown for information; not scored.
Know something about light & quiet here that we don’t? Tell us
Building
The materials a hotel was built and renovated with, how it handles damp, and what third parties have certified.
Low-emitting materials
Not yet reviewed.
Leak and mold response
Not yet reviewed.
Building certification
Not yet reviewed.
Shown for information; not scored.
Know something about building here that we don’t? Tell us
Notes & sources
- Hotel website: wellness and spa, Undated · read 22 Oct 2026
- Hotel website: accommodation, Undated · read 22 Oct 2026
- Hotel website: sustainability, Undated · read 22 Oct 2026
- Hotel website: overview, Undated · read 22 Oct 2026
Room count: Not confirmed from the hotel’s own site. Hotel website (opens the hotel’s website)
Photographs: Six Senses Douro Valley; Six Senses Douro Valley; Six Senses Douro Valley; Six Senses Douro Valley; Six Senses Douro Valley; Six Senses Douro Valley
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