What causes hot, bright pink hives and red rash on old sunburn?

Hello Ms. Heather.

Thank you for your query at DoctorSpring.com.

I understand your concern. Since you have psoriasis and a history of sunburn in that affected area, it is likely to be a new psoriatic lesion.

Psoriasis exhibits a phenomenon known as "Koebner's phenomenon" wherein new lesions develop at the site of skin trauma. In your case, the sunburn would have caused trauma to the skin. However, in order to confirm and to provide my best opinion, I would like some additional details.

- Please mention the site of the red rash.

- How long has it been present?

- How long after the sunburn did it develop?

- A picture of that area will be really helpful in coming to a diagnosis.

Please reply to the above and upload a photograph of the affected area.

Thank you.

Can't get an image now, as the redness and inflammation have subsided. It was on my chest, shoulders and neck, ONLY where I had the burn, on my neck and shoulders, but not where the straps were when I first got the burn. It's very apparent that the rash was only in the area where the burn developed. The sunburn occurred in late May, so it's been over a month since I was burned, but I still show the tan. The hives developed today, after I came back inside from about a half hour in sun with my chickens in the back yard. I live in Texas, where it can get quite hot, so I water the yard where they free range. The rash/hives lasted approximately an hour and a half. It was very pink and mottled, but again, just warm/hot - no itching, no raised areas, no pimpling or blistering. I hope this helps! Best, Heather

Hello Ms. Heather.

Thank you for the additional information. It is definitely helpful. Its good to hear that the rash has now subsided. It rules out a new psoriatic lesion. What you had seems to be a mild sunburn reactivation reaction. It is an idiosyncratic(unique to an individual) reaction, commonly seen in patients taking methotrexate but it is possible for it to occur with other drugs. However, among the 3 drugs you are on, currently there are no reports of such a reaction with any of those.

The good thing is, it is transient and disappears on its own. You can apply an emollient cream or calamine lotion over the affected area for faster resolution.

You have to make sure that you avoid excessive sun exposure to prevent it from recurring.

Sun protection is the best defense against it and other damaging effects of UV radiations.

In this regard, I have the following suggestions:

-Please try and avoid sun exposure, especially between 10 am to 4 pm.

-If you are going out in the sun, please wear protective clothing, including wide-brimmed hats, sunglasses, and loose-fitting clothing with long sleeves and pants. Clothing made from tighter-woven, darker fabrics tend to provide greater protection.

-Apply adequate amounts of sunscreen with a sun protection factor (SPF) of ≥30. Use a sunscreen with both UVA and UVB protection. Use a generous amount of sunscreen. Ideally, apply it half an hour before exposure. Reapply regularly.

I hope this was helpful.

Let me know if I can assist any further.

Thank you.

Thanks for your feedback. As I don't have the same response with my plaque psoriasis (scaly rash in affected areas) and the affected location seems to subside, I will make sure to apply sunscreen to the area and keep watch. If there is any rash that seems unusual after refraining from sun and protecting affected locations from possible rash, I will advise. Best, Heather