How do you control a flare caused by stress?

I would say using the usual stress management techniques. Get therapy, relaxation techniques, exercise, talking to friends. My first flare spiraled out-of-control due to stress and I could never get it to a manageable level without piling on the meds.

As someone who does not flare with short term stress (I think the cortisol boost the stress gives me is nicely anti-inflammatory!) but then has flared during periods of long term adversity, exhaustion and sedentary lifestyle this is what I do...

1) Accept that the flare is there and that I will need meds to calm it - so far I have been lucky that that has worked eventually but I accept that one day I may need to go to stronger meds or surgery. I have gone too long without the right meds in the past and needlessly extended my suffering

2) Do everything I can to look after myself (much as Madpotter posted) without going over the top - more details below if you want to read on

3) Insist on stool testing and don't presume it is a standard flare - turns out I have had some c diff over the years that was just presumed colitis and steroids made me more ill

4) Over my 30 yrs or so with this disease this has usually led to a good period of remission and/or managed symptoms. However, consistency has never been my strong point and I have too often let myself drop into a state of no exercise and poor self-care - so I think aiming for consistency is important. When things happen such as bereavement, job loss etc, keep aware that this is the time when it is vital to employ the strategies that work for me (such as gentle exercise, regular eating, try to control emotional eating binges, getting off the net and to bed).

5) As far as breathing techniques - no deep mouth breathing - focussed breathing in through the nose and out through the mouth seems to be the best way for short periods for me

6) Acupuncture with a highly trained and empathic practitioner - very helpful for me but this is individual, not all will find it so - and if your earning capacity is reduced it can be too expensive

7) Hypnotherapy and CBT therapy - this helped me with the lingering anxiety that I did not have bowel control or that any pain or signal to defecate signalled incontinence. Once you have experienced soiling yourself your body and mind are of course going to be on high alert to stop it happening again as the majority of humans will associate soiling self with shame. Unfortunately I am among those people who will experience lose bowels with anxiety anyway (as I work in mental health I know from stats that approx 1 in 5 women and 1 in 12 men experience this when their fight/flight response is activated). Soiling yourself when under threat is thought to have been an adaptive response for a number of reasons, i.e - allow all energy to be diverted to limb muscles (digestion uses a lot of resources), disgust attackers (think Skunk), possibly this is why more women experience it (I won't go into here why it may have been developmentally more important for women than men to disgust attackers). Thus I use therapy and hypnotherapy to be less fearful because limiting going out for fear of soiling self leads to less exercise, less closeness with others - all risk factors for depression and more illness!

8) Not blaming myself!! From all my recent research this self-affirmation is helping me - My (our) genetics are such that my mucous barrier in my colon is easily breached and my immune system super active to try and kill what is in the wrong place. This is a price I am paying for adaptation to an environment that is at odds with how my ancestors lived together with some conflicting genetics. It is what it is....this is not about being a weak person who can't take stress. I am at least lucky enough to have the genetics that mean that my UC has so far responded well to immunosuppresants.

Wow, what a novel - this is what pred does to me
Wishing you all the best!

I love all the great ideas above.

I would also add

1). Reading a good book. I enjoy Janet Evanavich. She makes me laugh. I recently read Sycamore Row by John Grisham. Living in a book and living someone else's life helps me so much.
2) Mute your phone and only answer emergency calls. My family calls this "being quiet". They don't like it But they have to get over it. They, especially my mom, tend to stress me even more. Haha.
3) I nurture my spiritual side. I have a book called "Jesus Calling" that I won as a raffle prize at a fundraiser golf tournament. Haha (is that fate, or what?). This book is about God's presence and peace. The key word to me is PEACE. It often "speaks" to me. Today's message is "letting go". Boy, do I need to learn that! Sometimes I wish I lived in a bubble of peace.
4). I use essential oils. My favorite is Joy and I rub it over my heart and behind my ears and on my wrists. I find that the happier I feel the less stressed I feel. There is also a blend that I use called Stress Away.
5). I cuddle with my cat and try to imitate him. He stretches, yawns, curls up in a sunny spot and shuts the world out.

Best wishes for less stress.

All of these methods can be effective ... or you can just use certain drugs or supplements. I had good success with Bupropion and also with a low dose of Doxepin (5 mg) which was prescribed by a psychiatrist for me. I also later had success with Valerian root extract too.