2025-10-20 21:00:00
An honest attempt to describe what you're technically supposed to do if you follow the posted policies. I don't think anyone actually expects you to do this!
Great to hear that you've decided to attend your first contra dance! It's really easy to get started, they're a lot of fun, and it's a friendly and welcoming community. You just show up, the caller tells you what to do, and in a few minutes you're dancing. It's got the best learning curve out there!
There's one minor exception, however, which is that some dances are "fragrance free". For these you'll need a little prep: plan to start getting ready about three weeks before your first fragrance free event. I know this can be a bit more time than you were expecting to invest before learning whether this is an activity you'd enjoy, but trust me: it's worth it!
It can be a little hard to figure out whether a dance you're considering attending is fragrance free. While some dances list it on the homepage, you can't count on that. For example, it could be at the bottom of the code of conduct or listed on a dance etiquette page. The safest thing to do is to read the whole website, but of course that's a ton of work so you might want to write to the organizers.
Once you find the policy, it probably looks something like:
These Dances are Fragrance Free - please do not wear perfume, cologne, or other scented products, as some of our dancers are chemically sensitive, and experience discomfort when exposed to these materials.
Read it carefully! While many people initially interpret these policies to prohibit perfume, "scented products" includes soap, shampoo, conditioner, deodorant, laundry detergent, etc. I recommend you start three weeks before the event, and spend a week noting the ingredients on each product you use. Read them over, looking for the words "fragrance" or "parfum". If you don't see those, there's still some chance that it's a scented product, unfortunately: sometimes individual fragrance ingredients are mentioned by name instead. I recommend taking a picture of the ingredients and uploading it to an LLM with a prompt like "are any of these ingredients fragrances"?
Note that some products will say "unscented", but still have fragrances. This is very confusing, but the basic idea is that an "unscented" product is intended not to smell like anything, and might include "masking fragrances" to cover the scents of the ingredients. Products that say "fragrance free" are a better bet, but the term is not heavily regulated and there are products out there like this eucalyptus lavender soap bar that say "free from any fragrances" but also have strongly scented essential oils:
Two weeks week before the event you should have your list of the products you need to find substitutes for. It's the same deal as before: analyze ingredient lists on potential replacements, and again LLMs may be useful. Here are some product lists that might be helpful in getting started: EastBayMeditation, FGC. If the cost is a burden, and a full set of personal care products can be a substantial investment, consider writing to the organizers to ask if they have a fragrance-free fund.
With medical products, like a medicated shampoo that happens to be scented, sometimes a fragrance free replacement is not an option. I'd recommend talking to the organizers: they may be willing to consider an exception. This is another reason to start early, since most of these events are organized by committees and can take a while to come to a decision.
About a week before the event you should have acquired all your replacement products: now it's time to start using them! The goal is that by the time you attend the event you no longer have any lingering fragrances on yourself or your clothes. For clothes in particular scents can last a long time, so the safest thing to do is clean your washing machine (wash the machine with baking soda, then again with vinegar) and then wash your clothes twice. If you use a laundromat there aren't any good options, since fragrance free laundromats are essentially not a thing, but if you ask around you may be able to find a friend who has their own machine and either already takes a fragrance free approach or is willing to help you out.
At this point, you're ready to attend the dance! Make sure you're wearing clothes that have been washed since you transitioned away from scented products. It's also a good idea to bring your own hand soap: it's sadly common for fragrance free dances to have scented products in their bathrooms. I hope you have a great time!
While this post is using satire to make a point, my core view is that it's fine for dances to have whatever approach to fragrances they choose as long as they're thoughtful about what they actually expect attendees to do and communicate it clearly. When I've written about this before I've read a lot of comments from people who don't see a problem with the status quo. My target with the satire here is dances that put a few words about a policy on their page that they don't actually expect people to follow, don't put effort into ensuring potential attendees see, and sometimes even blatantly subvert by having scented products available at their dances.
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2025-10-15 21:00:00
The situation in the contra dance world with "fragrance free" is a mess. Many dances have very strict policies, but they don't emphasize them. Which means they're not dances that work for people who need the strict policies, but at the same time are putting attentive and careful people through a lot of work in avoiding common scented products.
For example, if you look at the Concord Thursday homepage or FB event there's no mention of a fragrance policy. At the end of their Code of Conduct, however, there's:
Consider: We are a fragrance free event. Please do not wear scented products.
This isn't just asking people not to wear perfume or cologne: products not explicitly marketed as "fragrance free" generally have at least some scent. Trying to pick some very ordinary products that don't mention that they're scented on the front, when I read the ingredients they all list both "fragrance" and several scented ingredients (camphor, limonene, benzyl salicylate, etc):
Amazon
Basics Liquid Hand Soap
I'm not trying to pick on this one dance; it's common to have a policy like this without being explicit that the dance is asking everyone who attends to go out and buy new shampoo. Take the JP dance, which has, on their homepage:
These Dances are Fragrance Free - please do not wear perfume, cologne, or other scented products, as some of our dancers are chemically sensitive, and experience discomfort when exposed to these materials.
This suggests that by "scented products" they mean "things you wear specifically to give you a scent, but clicking through it's clear that they don't allow mainstream soaps, shampoos, deodorants, etc.
Some others I just checked:
One thing to keep in mind with these restrictions is that the impact is partially along racial lines. It's much easier to find fragrance-free products for white-typical hair; people with tightly curled or coiled hair are going to have a much harder time. Fragrance free products for these hair types do exist, but it's a significant investment to find them and figure out what works for your particular hair. There's also an interaction between race and culture, where in some communities, disproportionately black and hispanic ones, wearing scents is just a normal part of being clean. A lot of communities with these policies also worry about why their dance community is so much whiter than the area, and while I don't think this is a major contributor I also doubt it helps.
I've raised this issue before, but it didn't seem to have an effect, so I'm going to try a different approach of suggesting a range of alternative approaches that I think would be much better:
Say "fragrance free" and mean it. Include it in all your publicity the same way you would "mask required". Spell out what this means in terms of how to find products. I don't know any dances taking this approach.
Say something like "no perfume or cologne: don't wear products intended to give you a scent". This is the approach Beantown Stomp has taken.
Don't have a policy, accept that most people will show up having used scented products and a few will show up strongly scented. This is the approach BIDA uses.
I normally try pretty hard to follow rules, but this is one I dont' fully follow. My impression is that few attendees are taking the policy literally, and I don't think they actually mean that I shouldn't attend if I washed my hands after using the bathroom at a gas station on the drive over. I don't like this situation, however, and I think, as with speed limits people are used to ignoring, this approach is corrosive to the important norms around respecting policies. If you currently have a simple "fragrance free" somewhere on your website, consider one of the alternatives I suggested above?
EDIT: there's some discussion around what fraction of the population needs this kind of policy, with someone linking a CDSS document which says "chemical sensitivity is an invisible disability that affects around 30% of the population". I realized I have some relevant data on this: when I used to organize Beantown Stomp we had a "low fragrance" policy:
Some dancers are sensitive to fragrances, so we'd like to keep this a low-fragrance environment. Please don't wear perfume, cologne, body spray, or other products intended to give you a scent. If your shampoo, conditioner, deodorant, or laundry detergent are mildly scented, however, that's ok.
On the registration form we asked dancers to choose one of:
In 2020, 3% of dancers chose (a), 97% chose (b), and no one chose (c). This isn't the same as polling on a true fragrance free policy, but I would expect to see an even larger discrepancy there, where most people who would benefit from a "fragrance free" policy are covered by policies prohibiting "products intended to give you a scent".
2025-10-13 21:00:00
A dance organization I help run, BIDA, recently ran a survey. Several of the questions asked how folks felt about using far UVC and glycol vapors to reduce risk from COVID, flu, and other airborne pathogens. There were 208 respondents, which is pretty good!
When asked how their attendance would change if BIDA used these interventions, the response was:
| Unchanged | Increased | Decreased | |
|---|---|---|---|
| Far UVC | 75% (153) | 25% (50) | 1% (1) |
| Glycol Vapor | 77% (156) | 14% (29) | 8% (17) |
There were also free response answers, which you can read in the full writeup, on the BIDA blog. Summarizing them:
On far UVC, the person who said their attendance would decrease didn't give a comment giving more detail. The other comments were broadly supportive (~54) people, followed by neutral (~18 people), uncertain and wanting more information (~11 people), and skeptical that the lamps would actually reduce infections (~9 people).
On glycol vapors, the most common response was generally positive about more ways to reduce infection (~37), followed by wanting more information (~19), not caring (~17), strongly disliking the idea (~14), and more complex views (~10).
These results show a community that's strongly in favor of far UVC, which makes a lot of sense to me. The efficacy of UVC is proportional to sight lines, since it's beams of light, so it's a great fit for a big room with a tall ceiling. We'd need four lamps, which would cost $2,000. This is a meaningful amount of money, but with a total of 5,400 admissions at our dances in the 2024-2025 season and the lamps lasting at least 5y it's ~3¢/person-hour. For comparison, we spend about ten times that much per person-hour to provide people with disposable N95s.
The situation with glycol vapors, however, is much less clear. The evidence on safety is if anything stronger than on far UVC, and it's incredibly cheap (a $50 gallon of Triethylene Glycol is good for about 2y of dances). But we also have a significant number of people who don't like the idea (8% saying they'd attend less; ~14 negative comments out of 97). Reading through the comments I think some objections would turn out not to be an issue once people had experience with glycol vapor:
"I don't know much about them, but the CDC says they can irritate eyes and lungs": the level in the air is very low, and no one reported irritation at the trial dance.
"I have a sensitive nose and an aversion, sometimes reaction, to strong scents, especially chemical ones. I am deeply grateful for the fragrance free policy and am worried that this may adversely affect my experience and ability to attend and that of those similarly situated": Similarly, no one reported being able to smell the vapor at the trial dance. But BIDA also doesn't prohibit fragrances, and it's common for dancers (especially newer dancers) to wear scents, so I'm a bit confused about their reference to a 'fragrance free policy'.
Other objections, however, are from a perspective where experience wouldn't be relevant:
"I absolutely would not attend any event that had this in the air."
"I'm not comfortable with chemicals being deliberately pumped into the air by a DIY project. If there is a commercial system on the market using this technology, that would change my opinion."
All this has me feeling like I shouldn't push for us to deploy glycol vapors now, and the key thing is getting a commercial system on the market to address concerns. But then I go back and read the comments of people who are really positive on them:
"It would GREATLY improve my safety, comfort, and enjoyment!!! I hope other dances can also take these same precautions! Thank you for doing this work. (I LOVE SCIENCE when it's used for good. Thank you for this work!)"
"I would be more comfortable and feel safer, to the point where I might be okay with dancing unmasked."
"Also strongly in favor, for the same reasons. Let's do both!"
"Increase safety comfort and enjoyment so so so much!!!"
Overall I'm really torn on glycol vapors: the community is, on balance, in favor of them, and I think the evidence is really positive. On the other hand I also respect people having a high bar for evidence for things you breathe in. The board hasn't met to talk about this yet, and I'm not sure which way I want to push. Thoughts?
EDIT: in the comments people brought up the idea of having glycol vapors at only some dances. This could allow people with strong opposition the option to keep dancing while others could still get the benefits about half the time. If we did this, it could be either just the masked dances (to offer an extra safe option) or just the unmasked dances (to bring up the level of safety): which might be more popular? I categorized the responses (script) to look at the relationship between whether someone preferred more vs less masking and whether their attendance would go up or down with glycol vapors.
I started with the full 208 responses, discarded two people who said they didn't dance at BIDA because they didn't live in town, and then discarded another six who didn't answer all four of "I currently attend BIDA: ___", "If we started requiring masks at all our dances, I would attend: ___", "If we stopped requiring masks at any of our dances, I would attend: ___", and "If BIDA added Glycol Vapors, my attendance would: ___". This left me with 200 responses. I considered a response as inconsistent on masking if they said they'd attend more if we always required masks and also more if we stopped ever requiring masks, and also as inconsistent if it was the other way around. Here's what I found:
| attendance with masks | |||||
|---|---|---|---|---|---|
| higher masked | no change | higher optional | inconsistent | ||
| attendance with glycol | increase | 14 | 5 | 8 | 2 |
| same | 29 | 53 | 69 | 3 | |
| decrease | 4 | 5 | 8 | 0 | |
Looking at the table, if we were going to have glycol at only either mask-required or mask-optional dances it should be the mask-required ones: 30% of dancers who prefer masked prefer glycol vapors, vs 9% of dancers who prefer mask-optional and 8% of who said masking changes wouldn't affect their attendance. I also looked over the free text responses, and a large majority of the people with the strongest objections to glycol vapors preferred less masking.
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2025-10-08 21:00:00
A pandemic that's substantially worse than COVID-19 is a serious possibility. If one happens, having a good mask could save your life. A high quality reusable mask is only $30 to $60, and I think it's well worth it to buy one for yourself. Worth it enough that I think you should order one now if you don't have one already.
But if you're not convinced, let's do some rough estimation.
COVID-19 killed about 0.2% of people (20M of 8B). The 1918 flu killed more like 2.5% (50M of 2B). Estimating from two data points is fraught, but this gives you perhaps a 0.02% annual chance of dying in a pandemic. Engineering could make this much worse, especially given progress in AI, but let's set that aside for now to make a more conservative case.
A reusable mask ("elastomeric respirator") would be really valuable to have, if things got really bad. Let's imagine they cut your risk of dying by half: the rated efficacy is much higher (99%+) but real-world use isn't perfect, especially over the months or years another pandemic could last.
A mask should last at least ten years if unused, and over that decade it would drop this conservative estimate of your risk of pandemic-induced death from 0.2% to 0.1%. If you, as the US DoT does, value not dying at $14M, then this is worth $14k. Even if the benefit of a mask is 100x lower than we estimated ($140), it's still worth it to buy one.
I like geeking out over masks and there are a lot of options. I have a bunch of models, and if you'd like to come try them sometime (next EA Boston meetup on 10/26?) I'd be happy to show you what they're like. But if you just want to pick one and be done with it, leaving it in a box that you more likely than not don't need to open, a time tested but somewhat garish option is the 3M 6200 mask in Small ($17), Medium ($15), Large ($19) plus a set of 3M 2091 p100 filters ($7/pair):
I'd also recommend buying one now instead of trying to notice when a pandemic is coming: buying now ensures you get one instead of scrambling when everyone else is competing over a supply that can't keep up, and everyone who prepares ahead of time helps reduce shortages when a disaster comes.
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2025-09-09 21:00:00
Entropic Thoughts recently reanalyzed the data I'd shared on the relationship between mask requirements and dance attendance we've seen at BIDA. They conclude:
Other sources account for most of the variation in dance attendance, and masking only plays a small part. The amount of the total variation contributed by masking requirements is 5 %. This number is called the coefficient of determination, and its square root is the correlation: 0.21. This correlation is low enough that we cannot conclude that masking has a significant effect on attendance.
...
"But it still looks like masking has an effect!!" It does. It's just that if the effect is there, it is small enough that we cannot statistically prove an effect with just 44 dances. Assuming the coefficient of determination really is 5 %, and we are aiming for a traditional significance level of 0.05, the sample size curves tell us we would need over 80 dances to be sure of the effect of masking.
The approach they took in their post involves some statistics that make assumptions about the distribution of the data. While these assumptions may well be right, now that we have fast computers we can often use simulations to avoid this. I decided to have a go at analyzing this data with a permutation test.
In this approach, you permute (shuffle) the labels and then check what fraction of permutations led to an outcome at least as extreme as observed. In this case the attendance numbers were:
I decided to operationalize "at least this extreme" as the ratio of the average attendance at mask required to mask optional dances and wrote some code to simulate. With 10M simulations, which coded in very lazy python run for 27s on my Mac, I found that 19.3% of simulations passed that test, which can be expressed as p=0.193.
The bottom line is the same, however: while the pattern we saw is more likely in worlds where mask-optional dances are more popular, there's enough variation from other sources that with 23 dances there's still a decent chance that this apparent difference isn't real.
2025-09-08 21:00:00
We planned to trial far UVC and glycol vapors at the BIDA contra dance last night: these are two options (beyond masks and ventilation) for reducing infectious aerosol inhalation. Both worked without issues.
I set up the far UVC Aerolamp on the stage, slightly angled down, primarily aiming to clear the air above the dancers:
And the glycol vapor, 1 part TEG to 3 parts water by weight, in an ultrasonic humidifier. This went right in front of the intake fan: [1]
Logistically neither was much hassle, and we didn't get complaints about either. I would really like to measure how well they're working, but all the experiments I can think of (measuring the decrease in viable airborne bacteria?) are serious investments.
I also measured CO2 levels with my M2000 [2]:
These are high CO2 levels: this was our first dance back after the summer and attendance was high. Looking at our attendance sheet, I count 265; I'd guess occupancy peaked at ~230 since some people leave early, others arrive late, and some people are in the entryway and bathroom.
One thing you'll notice on that chart is that we kept the hall for some extra time at the end to measure longer. We'd like to estimate how much fresh air we're bringing in with the fans, and one way to do this is to fill the air with something (in this case, the CO2 people exhale) and then measure how quickly it decays:
I had Gemini and GPT-5 fit an exponential decay constant, and both gave me k=0.095. You can see it's not a perfect fit: it decays more quickly initially, and then decreases. I think this is because while the room has some mixing (with ceiling fans), it's not perfectly mixed.
With primary dimensions of 62x47ft and a height of ~20ft, I get ~5,600 CFM (62 * 47 * 20 * 0.095). At last night's (higher than usual) attendance this is 24 CFM/person.
The actual amount of fresh air people experience will vary a lot across the hall: I measured in the corner farthest from the incoming air. Overall, then, I think this is an underestimate of the amount of ventilation the typical person is experiencing.
(A different reason why I'd like to know how many CFM we're getting is to estimate how much TEG to vaporize. I'd previously guessed 8,000 CFM which still seems plausible: some portion of the air we're bringing in is going to go in one door and out the other without very thorough mixing.)
Next step will probably be a survey to understand how the community feels about applying these regularly going forward.
[1] We lent the fan out during the summer, which we've never done
before and generally try to avoid with our gear. It came back with a
busted switch. Thanks to Al for fixing it, in about 25 minutes before
the dance started!
[2] I also tried using Harris' Aranet4, but because I didn't realize I needed to switch it to 1-min sampling I didn't get very useful results.
