In fact, in cases of eczema, even a 30 C of sulfur can cause a flare up or aggravation. This often proceeds a disappearance of the eczema, although it might take a higher potency later.
The thing to do is not repeat the sulfur and report to the homeopath. IIf needed, the current dose of sulfur 30C can be antidoted, although in most cases this is not necessary if you can live with the rash until it dissipates. However, this should be monitored by your homeopath. In the case that a new symptom picture is emerging, a different remedy would be used, thus creating a "dynamic" antidote.
Do not use anything topically as this might interrupt the treatment and prevent cure. Unless approved by your homeopath. Calendula is usually safe, but even so, it can still be a sub-optimal choice compared to follow up for the correct remedy procedure.
A sulfur 30C rememdy does not have any sulfur in it, so it would not cause an allergic reaction.
There is no molecule of sulfur at a 12C potency.
I am a classical homeopath and I would be glad to offer further suggestions.
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