There is a custom followed , to blow off a candle kept at the top of the birthday cake.It is normally believed that if we make a wish and blow the candle the wish will come true.
As per Hindu traditions blowing off the candle is inauspicious .All functions begin with lighting the lamp and the lamp is kept lighted until the function gets over,even after the function the lamp is turned off by hand or some other material like flower and not by blowing off.
Light which is lit causes shining,anything that shines on its own makes other things to shine and acquire brilliance.To Hindus, darkness represents ignorance, and light is a metaphor for knowledge. Therefore, lighting a lamp symbolizes the destruction, through knowledge, of all negative forces.
Viewed spiritually the lamp has the concept of Goddess Lakshmi ,the goddess of prosperity offers praeyas(tranquility in this world) and Saraswathi,the Goddess of learning offers Sreyas(tranquility in other world).Darkness caused by sorrow and ignorance are removed by lighting the lamp.The radiance of the light spreads in the endless atmosphere.
So blowing off the candle invites ignorance and sorrow.Light the candle and move it to a safer place so that it does not get turned off.
Most acceptable solution would be to use oil stand lamp (Nila Vilakku) instead of the candle as we use in other Hindu functions because the polished and shining lamp and the light ignited by gingelly and other oil will attract germs and destroy them.Studies tell that candle light has got its own ill effects and can cause allergies,asthma and even cancer.
Asato maa sadgamaya
Tamaso maa jyotirgamaya
Mrityor maa amritan gamaya
Om shaanti shaanti shaanti
From the unreal, lead us to the Real;
From darkness, lead us unto Light;
From death, lead us to Immortality,
Om shaanti shaanti shaanti"
Source :REFLECTIONS ON HINDUISM BY H.H. SWAMI SATHYANANDA SARASWATHY