Hello,
Thank you for your query at DoctorSpring.com
Will it be possible for you to upload a picture of the rash?
Because what you describe is unique, and i need to see the rash in order to comment.
It can be an urticarial reaction, due to over activation of mast cells, triggered by certain situations.
Kindly upload the picture,
Regards.

Hello.
Thanks for your reply.

From your history, it seems to be chronic urticaria.
Urticaria is what is commonly referred to as hives.
It can be caused by allergy to food, medications, dust, pollen, animal dander etc.
When our body is exposed to a factor which it is allergic to, it's immune system is activated. Mast cells are a specialised type of immune system cells in our body which bring about an allergic response. Their activation leads to redness, swelling etc seen in allergic skin rashes. This is refererred to as an urticarial reaction in cases of urticaria.
In your friend's case, it follows a set pattern which is also possible in urticaria.

It's important to find out a causative factor in order to bring it under control.

However, it's more important to control the rash whenever your friend gets it. Otherwise it might sometimes progress to involve other parts of the body or might involve the nose and mouth, leading to their swelling, thereby causing breathing and swallowing difficulties.
It's not always possible to resolve the rash with treatment since its an allergy but it's possible to bring the rash under control.

For getting the rash under control, anti histamines like Allegra and Claritin are useful.

Please let me know if you have any queries.

Take care.