The membrane inside your nostril is going to be more sensitive than the skin on your face. If you can comfortably use a 50% solution on the spot on the face, (i.e. 1 part tea tree oil to two parts water), I would suggest that you begin with a 25% solution of tea tree oil for a pimple inside your nostril (i.e., 1 part tea tree oil to 4 parts water). If you still find this a bit too strong, you could come right down to a 10% solution (1 part oil to 10 parts water) to begin with. When diluting with water, it is best to mix the oil and water in a small container with a lid so that the two ingredients can be shaken together immediately before use. This is because the oil and water will naturally separate. If you only dip a clean cotton bud into the container (do not reuse a cotton bud after applying to your pimple), the solution will remain safe for use if kept in the fridge for up to a week.