When exposed to heat, i get bumpy skin and white bumps on my skin. is this serious?

No: It might be heat rash if they appear pale it is because fungal infection prevents tanning of skin - treat with combination of otc Hydrocortisone and antifungal cream.

May be hives: Some people get a physical hive caused by heat. Cool the area for quick resolution. If necessary you can pretreat with non sedating antihistamine such as Claritin (loratadine) orzyrtec.