- Causes & Risk Factors
- Symptoms & Signs
Facts you should know about lice vs. dandruff
- Lice infestations and dandruff, including infant/toddler seborrheic dermatitis (cradle cap), are extremely common.
- Scalp/hair infestations by lice are due to a parasite. Dandruff is due to excessively inflamed, dry, or greasy scalp changes.
- Common signs and symptoms for both lice and dandruff are itching and white structures on the scalp/hair shaft from either lice, nits, or dandruff (dried skin flakes).
- Diagnosis is straightforward and effective therapy exists.
What are lice?
Lice are small parasites that can affect three areas of the human body. Head lice (the subject of this article), body lice, and pubic lice (also known as crabs) are causes by three different but related parasites. Lice infestation occurs only in humans. Head lice infestation is by far and away the most common version of the three parasitic infections and is very contagious. Direct contact or sharing of items (fomites) that would touch the infected individual's hair/scalp is the primary mode of transmission from one person to another. Examples would include sharing caps, combs/hairbrushes, headphones, etc.
What is dandruff?
Dandruff, also called seborrheic dermatitis, is not an infection and not contagious. Rather it is a scalp abnormality that causes dry, scaly flakes to be shed in excess. Another manifestation of seborrheic dermatitis that may affect infants more frequently is commonly called cradle cap. This scalp change appears as scaly scalp areas that have a greasy character rather than the dryness of classical dandruff (which is not usually seen in infants or toddlers).
What are the causes and risk factors of lice infestations and dandruff?
Lice infestation is a person-to-person transmission of a parasite via contaminated agents (fomites) that facilitate transfer of the agent. Such agents would include caps, combs/hairbrushes, pillows, and headphones. Lice infestation is highly contagious and is very common in the toddler and early childhood grades. Between 6-12 million children from 3-11 years of age will develop a lice infestation annually. Crowded conditions, day care centers, and female gender (more likely to share hair brushes/combs) are risk factors. For reasons not fully understood, African-American hair is less likely to support a lice infection.
The presence of dandruff is extremely common. Many teen and adults have experienced such scalp changes. Some experience repeated exacerbations of the condition and may someday to be demonstrated to have a genetic predisposition to dandruff. Seborrheic dermatitis (cradle cap) is similarly a very common scalp situation found in the infant and toddler. Similar to dandruff, the situation may be of minimal consequence to some and a repeated experience to others. Neither condition reflects poor hygiene.
What are the signs and symptoms of a lice infestation and dandruff?
While both lice infestation and dandruff share common signs and symptoms, both may also occasionally appear without symptoms. Common elements include moderate scalp itching and small (2 mm in length) ivory white/opalescent material on the hairs shaft. Scalp lice infestation tends to occur predominately at the nape of the neck and may demonstrate immature lice (called "nits") attached to hair shafts approximately 1-2 cm from the scalp. Mature forms of lice (3-5 mm in length, resembling a mobile sesame seed) may be observed moving over the scalp surface. Dandruff affects the entire scalp and is unique (vs. lice) in that small white flakes are easily demonstrated on the shoulders after rubbing the scalp. The scalp of an infant with cradle cap will characteristically demonstrate the area to have a yellow greasy character that may be loosened and removed by scraping with a fingernail.
How do health care professionals diagnose a lice infestation and dandruff?
A history and physical examination allow accurate identification of the diagnosis. The characteristic changes in the scalp and examination for nits/mature lice help solidify the diagnosis. A Wood's lamp ("black light") may be used to facilitate demonstration of nits on the hair shaft. It is rare that a specialist (such as a dermatologist) would need to be consulted.
What are the treatments for a lice infestation and dandruff?
Treatment for lice consists of application of over-the-counter shampoos that contain either permethrin 1% (Nix, Rid, A200) or pyrethrin (Pronto). The former agent is generally used in that it kills both nits and adult lice whereas the latter is only lethal against lice (but not nits). In addition, permethrin products continue to be effective for several days after the shampoo is washed out. A repeat shampoo is recommended for both agents seven to 10 days after the first application. A prescription shampoo (ivermectin [Sklice]) is available if the above over-the-counter measures are not effective. Nit removal from hair shafts using a fine-toothed comb is worthwhile. Combs used to remove fleas from dogs and cats work well. All potential contact items (combs, caps, etc.) should be washed in water between 120-140 degrees. All other fomites (sofa cushions, pillows, towels, etc.) should be thoroughly vacuumed. The CDC recommends that all family members be screened for lice infestation and treated if demonstrated to be infected. Those not infected do not need to be treated.
Effective treatment of dandruff involves using an anti-dandruff shampoo (Head & Shoulders, T-Gel, etc.) that are effective but may require daily use to establish control of the situation. Infants and toddlers with seborrheic dermatitis (cradle cap) usually respond well to washing the scalp with routine baby shampoos. If the scalp is excessively involved, using the adult anti-dandruff shampoos detailed above may be safely used.
What is the prognosis for a lice infestation and for dandruff?
Both conditions carry an excellent prognosis. Repeated therapy may be required if the primary problem is not addressed (for example, not sharing hairbrushes). The symptoms (moderate itching of the scalp) are typically bothersome but not severe.
Is it possible to prevent a lice infestation and dandruff?
Following scalp/hair hygiene by not sharing items that may be contaminated by lice is effective prevention. Dandruff and/or cradle cap are not preventable at this time. However, they are only cosmetic by nature and not contagious and effectively treated by simple measures.
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United States. Centers for Disease Control and Prevention. "Parasites -- Lice -- Head Lice." Sept. 24, 2013. <https://www.cdc.gov/parasites/lice/head/>.
Weston, William L., and William Howe. "Overview of Dermatitis." UpToDate.com. Dec. 30, 2019. <http://www.uptodate.com/contents/overview-of-dermatitis>.
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