What a gorgeous smile!
DS1 had bad eczema as well, but it's a lot better now. DS2 shows no sign of it so far. I have battled it all my life, and spent my teens refusing to wear short sleeves and shorts (yes, even my arms and legs, as well as torso, were affected...

). I still suffer from it, but couldn't care less what people say or think, but the comments were really painful to hear as a young child/teen.
I don't know if this approach would work for you, but I would tell people right away what was "wrong" with DS so that I could avoid the stares/comments. At playgroup, I would just say "yep, it's a bad eczema flare-up, don't worry it's not impetigo or something else that's contagious...". Outside, I'd say "great, the sun will help his eczema" or "too bad it's windy, it's going to worsen the eczema..." I found that once people knew, they would leave it alone, and that way I didn't have to field questions. Also, DS1 is pretty comfortable with his condition now (at almost 4) and will use the same lines.
Slightly OT, be weary of cortisone/steroid creams - they can have serious side-effects, possibly worse that the actual eczema itself (yes, it's unsightly, but if the child tolerates it well, leave it alone...).
Hugs!