Yes, it’s a real thing – Toasted Skin Syndrome. Historically, this is from furnaces or stove tops, back in olden days, where people stood or sat too close to a fire and they got this very interesting pattern. It almost looks like brown marble cake on your skin. Now-a-days, you can become subject to toasted skin syndrome from a hot laptop that's on your lap for too long.
The only way to treat this, is to remove the heat source. Eventually, toasted skin syndrome will resolve on its own, as long as your skin's not being repetitively warmed. The brownness will go away soon enough! Toasted skin syndrome is actually just a result of hyper-pigmentation after inflammation. So, basically, your skin becomes inflamed because of the chronic heat source, and then it turns brown afterwards.