MOH said vulnerable individuals, including the elderly, pregnant women and those with chronic heart or lung conditions, should avoid outdoor activities when hourly PM2.5 readings are in the high band of 151 to 250.
Those who need to go outdoors for immediate activities may wear a well-fitting N95 mask or equivalent to reduce their exposure to haze particles.
When PM2.5 readings reach the very high band of 251 and above, healthy individuals should also minimise all outdoor activities. Those who need to venture outdoors may similarly use an N95 mask for protection.
However, MOH said N95 masks are generally not needed for commuting between home and school or work, or in indoor environments.
The ministry also cautioned that elderly people, pregnant women and those with severe heart or lung conditions who experience breathing difficulties should consult their doctor before using an N95 mask.
Those who experience discomfort while wearing one should take a break from using it.
Besides N95 masks, KN95, FFP2 and KF94 masks are also effective in reducing exposure to haze particles, MOH said.
Members of the public can visit the HazeMaskGoWhere website for more information on collection locations and live updates on mask availability at the vending machines.