Head lice

• Intense itching. An allergic reaction to the saliva that lice inject during feeding may result in itchy red bumps on your scalp, neck and shoulders. Some people, particularly if this is their first infestation, don't experience itching.
• Adult lice on scalp. The most common spots to find adult lice are behind your ears and along the back of your neck. Lice are tiny, about the size of a strawberry seed, but they can be up to 1/8 inch (3 millimeters) in size.
• Lice eggs (nits) on hair shafts. Nits resemble tiny pussy willow buds. Nits can be mistaken for dandruff, but unlike dandruff, they can't be easily brushed out of hair.

Causes

Head lice can't fly or jump, and they're not transmitted by pets. They spread by head-to-head contact or via contact with contaminated personal belongings or home furnishings.

Head-to-head contact

This is the most common mode of transmission and may occur as children or family members play or interact closely together.

Sharing personal items

Less commonly, head lice may be transmitted via such items as:

• Caps, hats and scarves
• Brushes and combs
• Hair decorations, such as barrettes
• Headphones

Home furnishings

Head lice may sometimes be contracted by contact with contaminated:

• Towels
• Clothing
• Blankets
• Pillows
• Upholstered furniture 

Risk factors

• The greatest risk factor for getting head lice is coming into contact with someone who already has lice. Cleanliness and personal hygiene have little bearing on whether you get lice.
• Young children, preschool through elementary age, are most prone to infestation, which often transfers to a child's family members. Females of all ages get head lice more often than males do.

Complications

Lice may cause you to scratch your head so vigorously that you break the skin. See your doctor if these scratches become infected.

Diagnosis

Lice cement their eggs very firmly onto the base of hair shafts, very close to the scalp. According to experts with the Centers for Disease Control and Prevention, nits found more than a quarter inch (6.5 millimeters) away from the scalp have either already hatched or aren't going to hatch. So simply finding nits isn't proof of an active infestation. The clearest sign is finding a living, moving louse. Combing wet hair with a fine-toothed comb is the best way to find this evidence.

References:

http://www.medicinenet.com/head_lice/article.htm

https://www.hse.ie/eng/health/az/H/Head-lice/

http://kidshealth.org/en/parents/head-lice.html

http://www.irishhealth.com/article.html?con=23

http://www.hedrin.ie