I'm Dr Jake Sloane and thanks for your question on here. The simple answer is yes, a small injection of either botox or dermal filler, depending on what treatment you wanted, could in theory be done on a discrete area of the body. However in practice these are never done as the products have such a good safety profile and the chances of you developing an allergy to either of these are extremely remote.
If you aren't allergic to albumin/eggs, you will be fine with Botulinum toxin. (It is mixed with albumin as a preserver in the manufacturing process)
Today's fillers are made of hyaluronic acid, a natural substance found in our own skin, albeit using a man made version of it. I have not heard of a true allergy to this, just redness which may have been caused by the act of the needle itself rather than the filler material.
For more information, please visit my website: http://www.drjakesloane.co.uk
or feel free to get in touch on my mobile: 07956 129103
Dr Jake Sloane