Browser-only scheduling tool
Almost everyone has been told to patch test. Almost nobody has been told for how long, with how much, on which patch of skin, or what to do about the four products they bought in the same order. Tick what you are about to start using and this builds the schedule, with every number either traced to a published protocol or marked as our own choice.
9 product classes, 6 cited sources, reviewed August 15, 2026
Build the schedule
Tick all of it, including the things you were planning to just start using. The number at the top of the result is usually the surprise, and it is the honest cost of finding out which product did something rather than that something happened.
Optional. Leave it blank and the schedule is numbered from day one.
9
days from the first application to the end of the last watch period
14
applications across 1 product
1.4 mL
of product used in total, at the standardized 0.1 mL per application
Where to put the test
the side of the neck, or behind the ear
Sourced ruleDermNet lists the side of the neck and behind the ear alongside the forearm as open application test sites. For a product going on your face, these are a closer match in skin thickness and in the amount of movement and friction the area gets.
What this site cannot tell you: The neck is a closer match to the face than the forearm is, but it is still a different area, and it is more visible, which is worth knowing before you start a test that might produce a red patch.
Source: DermNet, Open application test; Hannuksela and Salo 1986, The repeated open application test (ROAT), Contact Dermatitis
The schedule
How to apply: Apply the normal amount and thickness you would actually use, over the marked spot, and leave it alone. Do not wash the spot for the rest of that half of the day.
Why it sits here: Leave-on products stay in contact the longest and usually go on the largest area, so they are the ones worth clearing first. This is the exposure pattern the original ROAT was built to reproduce: a leave-on product, twice a day, on a fixed patch of skin. Seven days of twice-daily application is the protocol Hannuksela and Salo used, and it sits at the bottom of the seven to 10 day range the AAD gives consumers.
Source: Hannuksela and Salo 1986, The repeated open application test (ROAT), Contact Dermatitis; American Academy of Dermatology, How to test skin care products
The rules this schedule is built from
Two applications a day, morning and evening, for every product in the plan. That frequency is the protocol, not a rounding of it.
Source: Hannuksela and Salo 1986, The repeated open application test (ROAT), Contact Dermatitis; American Academy of Dermatology, How to test skin care products
Mark one spot and use the same spot every time. The AAD says quarter-sized, which works out at about 4.6 cm2 from the statutory 0.955 inch diameter; the ROAT standardization paper marks about 4 cm2. Those are the same spot in practice.
Source: American Academy of Dermatology, How to test skin care products; Practical suggestions to improve standardization of repeated open application testing (ROAT) for daily use products; 31 U.S.C. 5112, Denominations, specifications, and design of coins
About 0.1 mL per application in the standardized protocol, which is roughly what a normal-thickness layer over that spot comes to. The AAD phrases the same instruction as the normal amount and thickness you would actually use.
Source: Practical suggestions to improve standardization of repeated open application testing (ROAT) for daily use products; American Academy of Dermatology, How to test skin care products
Keep looking at the spot for 2 days after the last application. That a tail is needed at all is sourced: an allergic reaction is often only evident several days after the substance goes on, and reactions in the standardized protocol usually appear around day 4. The exact length of the tail is our choice.
Source: DermNet, Open application test; Practical suggestions to improve standardization of repeated open application testing (ROAT) for daily use products
One product at a time. If you start three new products in the same week and your skin objects, you have learned that something is wrong and nothing about what.
Immediate stinging on application is usually irritation rather than allergy. The reaction this test is built to catch is the delayed one that turns up days later.
Source: DermNet, Open application test
Stop at the first sign of a reaction rather than finishing the schedule. The original protocol ran for 7 days unless dermatitis appeared earlier, and the AAD says to gently wash the product off as soon as possible and not use it again.
Source: Hannuksela and Salo 1986, The repeated open application test (ROAT), Contact Dermatitis; American Academy of Dermatology, How to test skin care products
This planner schedules a test. It does not diagnose anything, it cannot predict how your skin will respond to a product, and a clear result is evidence rather than a guarantee. If a reaction spreads beyond the test spot, does not settle after you stop, or worries you at all, that is a question for a clinician and not for a web page. Nothing you type here leaves your browser.
The instruction nobody finishes
Read the back of enough packages and you will find the same two words with nothing attached to them. Patch test first. It appears on labels, in reviews, in the replies under every skincare post, and it is almost always the end of the sentence rather than the start of one. Test where. For how long. Twice a day or once. What counts as a reaction. What do you do about the fact that you bought a cleanser, a serum, a moisturizer, and a sunscreen at the same time and would quite like to use them this month.
Those answers exist. They have existed since 1986, when Hannuksela and Salo published the repeated open application test in Contact Dermatitis: apply the substance twice daily for seven days to the flexor aspect of the forearm near the crease of the elbow, unless dermatitis appears earlier. That is a protocol. It has a site, a frequency, a duration, and a stopping rule, and it was validated against clinical patch testing in 86 patients. Of the patients whose clinical patch test result was questionable, 44% turned positive on the open application test.
What the advice on the package is gesturing at is a real method. What people usually do instead is dab a bit on their wrist, look at it for ten minutes, and declare victory. Those are not the same activity, and the gap between them is what this planner exists to close.
Twice a day, for days
Seven days of twice-daily application in the original protocol. Seven to 10 days in the guidance the AAD writes for the public. Both agree on the frequency, and both are describing something you commit to rather than something you do while the shower warms up.
The standardized version of the protocol notes that reactions usually develop at about four days, which is roughly four days after most people have stopped looking.
One marked spot
The AAD says a quarter-sized spot somewhere the product will not be rubbed or washed away. The standardization paper marks about 4 cm2 with a stencil and dispenses 0.1 mL from a 1 cm3 syringe. A US quarter is 0.955 inch across by statute, which is 24.26 mm, so its area is about 4.6 cm2.
A consumer instruction and a research protocol, arrived at independently, pointing at the same patch of skin.
Stinging is not the signal
DermNet separates the two things people conflate. Immediate signs of irritation are usually irritant contact dermatitis. The allergic reaction the test is built to catch is often only evident several days after the substance goes on.
Which means the ten-minute wrist test is not a fast version of a patch test. It is a test of a different thing.
The arithmetic people avoid
Here is the part the advice never says out loud. If you test one product at a time, seven days of applications plus a short watch period each, four new products is about a month before the last one is cleared. Run the planner on a full routine and it will tell you the number rather than let you discover it in week three.
That number is why nearly everybody quietly skips the step. It is also why the step, when skipped, produces nothing. Start four products in the same week, react to something on day five, and you have four suspects, no way to rank them, and a strong temptation to abandon all four and blame the most expensive one. The month is not the cost of testing. The month is the cost of getting an answer instead of an event.
So the planner does two things with that. It shows you the real total up front, and it orders the queue so the products that matter most go first. Leave-on products go before rinse-off ones, because a moisturizer sits on a large area of skin for hours and a cleanser is on for under a minute. If you run out of patience halfway through, you will at least have run out of it in the right order.
The second thing it does is offer a compromise instead of pretending nobody needs one. Two products can run at once on two clearly separated sites, left and right, which roughly halves the calendar. That is our own scheduling choice rather than something a paper prescribes, and the tool marks it as ours.
We cap it at two on purpose. The single thing an open application test gives you that a general sense of unease does not is attribution: this spot, this product. Put four tests on one forearm and the sites crowd together, a reaction spreads across more than one, and you are back to knowing that something happened. Two sites, far apart, is the most you can run and still get the answer you started the test for.
There is a third option that the planner cannot schedule for you, and it is worth saying anyway. Buy fewer things at once. A queue of one is a seven day queue.
What the label does not do for you
The most common reason people skip a patch test is that the package already told them it was fine. Hypoallergenic. Dermatologist tested. For sensitive skin. It is worth knowing exactly how much weight those words carry in the United States, because the FDA has published the answer and it is shorter than most people expect.
There are no Federal standards or definitions that govern the use of the term hypoallergenic. The agency goes further and states that it knows of no scientific studies showing that cosmetics making that claim, or similar claims, actually cause fewer adverse reactions than competing conventional products. Manufacturers may use the term without supporting evidence. The same absence of a legal definition applies to fragrance-free and to for sensitive skin.
None of that means such products are worse, and it is not an accusation aimed at any brand. It means the claim is a description a company chose rather than a threshold it cleared, so it cannot do the work people ask it to do. The two things that actually carry information are the ingredient list, which is required, and what happens when the product meets your skin over a week.
There is one honest simplification available. A shorter ingredient list is a shorter list of things to have a reaction to. That is arithmetic rather than a claim about safety, and it is the reason a single-ingredient product is an unusually easy thing to test: whatever the result, you know what produced it.
Scope
It is a scheduling tool. It does not diagnose anything, it does not tell you whether you are allergic to a product, and it does not perform the diagnostic patch testing a clinician carries out with standardized allergens under occlusion. Those are a different procedure done by a different person for a different reason.
It does not rate or rank any product, ours included, and it makes no claim that any product treats, prevents, or improves a skin condition. It cannot predict how your skin will respond to anything, because that depends on things no web page has access to.
It does not invent numbers. Where a document gives a site, a dose, a frequency, or a duration, the planner uses it and links the document. Where we made a scheduling choice inside a published range, the output says so on the rule itself rather than dressing it up as evidence.
Where a product label gives its own directions or its own test instructions, follow the label. If a clinician has given you instructions, follow those instead of this. And if a reaction spreads, persists after you stop, or worries you, stop reading web pages about it.
Nothing you enter is sent anywhere. The schedule is calculated in your browser and nothing is stored.
Common questions
Twice a day for seven to 10 days is the range the American Academy of Dermatology gives consumers, and seven days of twice-daily application is the protocol Hannuksela and Salo used when they published the repeated open application test in 1986. The planner uses seven days for straightforward leave-on products and 10 for actives and acids, and it labels the second of those as our own choice within the published range rather than a rule from a document.
The forearm is the studied site. The original protocol used the flexor aspect of the forearm near the crease of the elbow, and the AAD tells people to use the underside of the arm or the bend of the elbow. DermNet also lists the side of the neck and behind the ear, and for a face product those are a closer match in skin thickness and in how much friction the area gets. The planner offers the neck for face products and the forearm for body products, and it says plainly that neither site stands in for an eyelid.
The standardized version of the protocol uses 0.1 mL per application on a marked area of about 4 cm2. The AAD phrases the same instruction without a number: use the normal amount and thickness you would use if you were applying the product regularly, on a quarter-sized spot. A US quarter is 0.955 inch across by statute, which is 24.26 mm and works out at about 4.6 cm2, so the two instructions describe the same patch of skin.
You can, and most people do, and it is the reason so many patch tests produce no useful information. If you start four products in one week and your skin objects, you know something is wrong and nothing about what. The planner defaults to one at a time and offers a two-site mode capped at two products on clearly separated sites, because past two the sites crowd together and attribution stops working, which was the whole point.
Usually not. DermNet draws the distinction directly: immediate signs of skin irritation are usually irritant rather than allergic, while an allergic reaction is often only evident several days after the substance is applied. That is why the schedule runs for days rather than minutes, and why it keeps you looking at the spot after the last application rather than declaring the product clear the moment you stop.
No, and any tool that tells you otherwise is overselling itself. A clear result is evidence that this product, at this dose, on this patch of skin, over this many days, did not produce a visible reaction. It is not a prediction about a larger area, a different season, a different formulation batch, or a delayed response outside the window. This planner schedules a test; it does not diagnose anything and it is not the diagnostic patch testing a clinician performs.
The FDA is unusually blunt about this one. There are no Federal standards or definitions that govern the use of the term hypoallergenic, and the agency states it knows of no scientific studies showing that products making the claim cause fewer adverse reactions than conventional products. The same absence of a federal definition applies to fragrance-free and to for sensitive skin. The label is a marketing decision, so the ingredient list and your own test are what you actually have.
Stop rather than finish the schedule. The original ROAT ran its seven days unless dermatitis appeared earlier, and the AAD says to gently wash the product off as soon as possible and not use it again, with a cool compress or petroleum jelly to relieve the skin if needed. If a reaction spreads beyond the spot, does not settle after you stop, or worries you, that is a question for a clinician rather than for a planner.
An easy thing to test
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