Spray vs. Applied Gel Deodorants
Like I already stated, HS is a disease marked by pain and swelling and anyone who has had a rash under your armpit knows that once there is the pain in that area, any further touching of that region will only make it worse.
One of the most traumatic things that you could do would be to apply solid gel deodorant to your underarm.  Without a doubt, patients that do use deodorant when having to deal with an HS flare-up testify that deodorant sprays are more tolerable because they don't require direct contact to the surface of the skin.
Be cautious though, because many spray deodorants are alcohol-based and if you apply this to an active infection, you will have a sudden intense spike of pain as the alcohol makes contact with your skin. Most deodorants also naturally dry out the skin. For this reason, if you can avoid applying deodorant for a day or two, the best course of action for you would be to try to avoid deodorant entirely until your flare-up subsides slightly. 
If you are someone who suffers from flare-ups for a prolonged period or you are just not a fan of body odor, it is no surprise that going through a day without using deodorant is not an option for you.
One type of deodorant that seems to be popular with patients suffering from HS is Crystal brand deodorant. To avoid any confusion, this is not a deodorant composed of crystal products, it is just named Crystal so be careful when you are searching for the product, it can get a bit tricky.
Crystal brand deodorant is believed to be effective for patients suffering from HS because of what this d is deodorant does not contain. Studies show that HS flare-ups tend to worsen when patients are exposed to aluminum, a common ingredient in over 90 percent of the deodorants that are on the market nowadays. Aluminum is a common allergen that can cause skin inflammation, and when patients with already pre-existing skin problem come in contact with aluminum, their rash will only get worse. 
Crystal brand deodorant is a product that is aluminum and paraben-free and is also available in spray containers so it is no surprise to hear that this is a potentially effective deodorant option for patients suffering from HS.
"Arm and Hammer" Essentials Natural Deodorant
Another product that has received praise from patients suffering from HS would be Arm and Hammer's Essential Natural Deodorant. This is another type of deodorant that lacks and aluminum and parabens which are known to worsen skin conditions. You've already heard a little of why aluminum is not good for patients with this condition, but what exactly are parabens?
Parabens are a type of preservative that are commonly found not only in hygiene and cosmetic products, but also in medications and foods that we eat. Much controversy about this product has been reported recently because of the link to cancer that these products may have. Although the exact mechanism is not entirely understood, early findings show that parabens have an agonistic effect on estrogen. This effect means that parabens stimulate the body to produce more estrogen which can become quite detrimental for patients suffering from HS. 
We already know that HS seems to be worse in teenagers going through puberty. The changes in the apocrine glands because of testosterone and estrogen are believed to be the reason why this can be so traumatic for patients, but when natural products add extra topical estrogen to areas, it is no surprise patients report that the flare-ups worsen. That is why it is better for patients to avoid this type of ingredient when they are suffering from HS. 
Some deodorants may be more effective than others, so it is up to you to conduct your experiments to determine what hidradenitis suppurativa treatment is right for you and helps you decrease your flare-ups. All in all, the brands of deodorant may not be the most important thing to consider here. The take-home message that you should learn if you are looking for a deodorant to use if you suffer from hidradenitis suppurativa would be one that does not contain aluminum or parabens. Some may be more effective than others, so it is up to you to conduct your own experiments to determine what