Bumps that turn up most nights on one arm or the other usually point to insect bites rather than a skin condition. Bed bugs and mosquitoes are the common culprits in hostel settings with shared mattresses or bedding, and these bumps are typically itchy, raised and fade within a few days on their own.
Next Steps
Check your mattress seams and bedding for tiny bugs, and wash your sheets in hot water. Keeping nails short and using a cold compress helps the itching without risking a skin infection from scratching.
Health Tips
See a dermatologist or physician if the bumps spread quickly, blister, or come with swelling of your lips, eyes or face, or any difficulty breathing.