What is the balance of advantage?

If wearing a helmet is the difference between you having the confidence to cycle (or to cycle more) or not, you should wear one! The health benefits of cycling outweigh greatly any negative consequences of helmet use.

On the other hand, if wearing a helmet makes it likely that you will cycle less, then the balance of advantage is cycling without a helmet.

If helmet wearing is unlikely to affect the amount you cycle, you may like to consider the following. Interpretation of the data can be controversial, but examination of the wider evidence from places where helmet use has become significant suggests that the following are reasonable conclusions:

If worn correctly, a cycle helmet may afford some protection against minor, largely superficial, injuries to the head.
A helmet is unlikely to offer protection against more serious or life-threatening injuries.
You are more likely to hit your head in a crash if you wear a helmet.
There is evidence that helmeted riders may crash more often (Erke and Elvik, 2007 has found a 14% increase in risk in Australia and New Zealand). This could be particularly the case if wearing a helmet makes you feel better protected.
A helmet may increase the very small risk of the most serious brain injuries that lead to death and chronic intellectual disability.
The likelihood of serious head injury when cycling is extremely small, and hugely outweighed by the health benefits of cycling.

In all cases you should regard learning to cycle skilfully as your most effective defence against injury of any kind.

Note: Reference to choice in wearing a helmet clearly does not apply where helmet use is mandatory.

References

Erke and Elvik, 2007

Erke A, Elvik R, 2007. Making Vision Zero real: Preventing pedestrian accidents and making them less severe. TOI, Norwegian Centre for Transport Research Report 889/2007.