There are 10 words that start with 'lacto'.
| lactone | lactose | 
| lactones | lactonic | 
| lactoses | lactogenic | 
| lactobacilli | lactobacillus | 
| lactoglobulin | lactoglobulins | 
Note: These 10 words that start with 'lacto' are found from the USA & Canada version of the tournament Scrabble word list.