Autumn could herald a slump in blood stocks, donor chiefs fear.
Now people across Keighley district are being urged to attend sessions this month to boost supplies.
NHS Blood and Transplant said dark nights and the onset of the cold and flu season can have an impact.
Spokesman, Donna Batty, said: “It can be tempting to stay indoors at this time of year, but we would ask people to fight the urge to hibernate and save lives instead.
“Colds and flu can have a knock-on effect with blood stocks, which is why we need people to act now.”
Donor sessions are planned at Victoria Hall in Keighley on October 11, between 1.15pm and 3.15pm and 4.15pm to 6.30pm; at Haworth Community Centre, Butt Lane, October 27, 10.15am to 1.45pm; and at Silsden Methodist Church on October 31, 2.30pm to 4pm and 5pm to 7.30pm.
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