I had a reaction to the deodorant.
Sodium bicarbonate and palmarosa essential oil are two ingredients that are naturally very effective at fighting the growth of bacteria, which are responsible for body odour. That's why they're used in many natural deodorants. It's possible that your skin has a reaction to one of these ingredients.
Having said that, while some people's skin may react to these ingredients, they are not dangerous in any way – whereas some ingredients used in deodorants might be, such as aluminium salts.
One way to avoid reactions is to apply a very fine layer of product each time, so that it's not too much for the skin. Or you could alternate with another deodorant.
If you still have a reaction even when you've tried this, it may just be a reaction to the product, or you may be allergic to sodium bicarbonate or the essential oils. In that case, of course, we suggest you stop using the deodorant!
To help your skin recover, you could apply some botanical oil to your underarms.