Stewart laughs as she recalls those early days. “It's so intimate! I would never say who I waxed.” Discretion is a cornerstone of her success. When cast and crew returned to the western Canadian province – this time to Vancouver, where Stewart had moved to – to shoot X-Men follow-up X2, the producers remembered her loyalty and secured her services for the sequel.

These days she's busy with the stars of American television series Riverdale and A Series of Unfortunate Events, and another show with a name that's changed so many times during filming she just refers to it as “that show”. She's not fussed by names or celebrity. (When production companies book appointments, they rarely use a client's real name anyway.)

She's always prepared to deal with specific conditions that working actors and actresses subject their skin to – thick, waxy, occlusive make-up that causes clogged pores, breakouts and inflammation, and environmental stressors from working in extreme conditions – pouring rain, howling wind, unforgiving sunlight – sometimes for hours.

One actress was recently sent to Stewart with a large semi-circle of darkening, peeling skin on her face. Her make-up artist thought it was a skin reaction but it turned out to be a burn from hot spotlights that had been focused intensively on her face. Another actor, who was co-starring in a period martial arts movie, went to Stewart to fix his skin, which had been made raw and swollen by the daily application and removal – using, respectively, strong adhesive and straight alcohol – of fake facial hair.

Stewart’s focus is on skin health. Everyone wants beautiful skin, but that's a by-product of healthy skin. To that end, she insists her celebrity clients follow a regimen of cosme-ceutical products that she custom-selects for each person. Among her favourite skincare products are iS Clinical's Pro-Heal Serum (antioxidant) and Active Serum (brightening); ZO Skin Health's Growth Factor Serum (fine lines and wrinkles) and Daily Power Defence (retinol); and AlumierMD's AluminEye (eye cream) and Ultimate Boost Serum (hydration).

Stewart would rather pass on a project than compromise on the results. While she treated cast and crew working on the first Deadpool movie, she turned down work on its sequel because she and the film’s producers couldn't agree on a budget that would allow for the full recommended scope of treatments and products.

Her fees aren't exorbitant – facials start at C$175 (US$132) – given that she needs to cover not only the cost of treatments but anticipate unforeseen costs such as those for 3am emergency calls; keeping staff available when clients are running late; or, as was the case during the filming of Doctor Strange, keeping her shop staffed and operational late into the night to accommodate the show's schedule.

A-list actors who are in Vancouver for filming negotiate treatments with Stewart as part of their contracts. Lesser actors are booked appointments by their production companies that cover a pre-negotiated range of treatments, which could include intense pulsed light sessions, oxygen treatment, and light therapy, in addition to her signature facial.

The most common problems Stewart sees in her TV and film clients aren't dissimilar from those people outside the entertainment industry experience: eye bags, breakouts and hyperpigmentation. One difference in their treatment is that these clients don't have the luxury of down time and often have to be back on set within 12 hours, or ready for a photo shoot or a to walk a red carpet.

For eye bags, aside from getting more sleep, Stewart's top recommendation is an LPG Endermolift (a non-surgical face- lifting and skin-tightening anti-ageing treatment) and her favourite collagen face mask from Swissline (exclusive to Stewart’s spa). For breakouts, she will reduce the swelling, remove the pus, make an extraction and have the blemish reduced by 80 per cent by the time the client walks out.

For hyper-pigmentation she uses a combination of low-level laser treatment and a special massage technique. While this doesn't sound particularly exciting, it's very effective and non-invasive; Stewart says she's had other aestheticians book this service, incognito, to try to copy her treatment.

Her Asian clients have even more specific requirements, as Asian skin easily hyperpigments and is prone to dehydration. “The [sonic face brush] ruined my Asian clients' skin,” moans Stewart. Such an aggressive cleansing tool can destroy the lipid barrier in some people, exacerbating dehydration.

However, Asian skin is also extremely responsive to changes in diet, so she always recommends Bend Beauty's Anti-Ageing Formula, a liquid supplement based on essential fatty acids that helps hydrate skin and improve its elasticity and texture.

Stewart’s number one skincare tip, though, regardless of status or ethnicity, is to drink plenty of warm water with lemon.

That's something everyone can do.