When skin is exposed to the sun constantly, thick, scaly, or crusty bumps appear. The scaly or crusty part of the bump is dry and rough. The growths start out as flat scaly areas, and later grow into a tough, wart-like area.

An actinic keratosis site commonly ranges between 2 and 6 millimeters in size, and can be dark or light, tan, pink, red, a combination of all these, or have the same pigment as the surrounding skin. It may appear on any sun-exposed area, such as the face, ears, neck, scalp, chest, backs of hands, forearms, or lips.

Classification

Actinic keratoses may be divided into the following types:

• Hyperkeratotic actinic keratosis
• Pigmented actinic keratosis
• Lichenoid actinic keratosis
• Atrophic actinic keratosis

See also:

• Actinic cheilitis
• Squamous cell carcinoma in situ

Prevention

Preventive measures recommended for AK are similar to those for skin cancer:

• Not staying in the sun for long periods of time without protection (e.g., sunscreen, clothing, hats).
• Frequently applying powerful sunscreens with SPF ratings greater than 30 and that also block both UVA and UVB light.
• Wearing sun protective clothing such as hats, long-sleeved shirts, long skirts, or trousers.
• Avoiding sun exposure during noon hours is very helpful because ultraviolet light is the most powerful at that time.

Diagnosis

Doctors can usually identify AK by doing a thorough examination. A biopsy may be necessary when the keratosis is large and/or thick, to make sure that the bump is a keratosis and not a skin cancer. Seborrheic keratoses are other bumps that appear in groups like the actinic keratosis but are not caused by sun exposure, and are not related to skin cancers. Seborrheic keratoses may be mistaken for an actinic keratosis.

Histopathology

Actinic keratosis usually shows focal parakeratosis with assocatiated loss of the granular layer, and thickening of the epidermis. The normal ordered maturation of the keratinocytes is disordered to varying degrees, there may be widening of the intracellular spaces, and they may also have some cytologic atypia, such as abnormally large nuclei. The underlying dermis often shows severe actinic elastosis and a mild chronic inflammatory infiltrate.

Treatment

Various modalities are employed in the treatment of actinic keratosis:

• Diclofenac sodium 3% gel, a nonsteroidal anti-inflammatory drug. Recommended duration of therapy is 60 to 90 days.
• Cryosurgery, e.g. with liquid nitrogen, by "freezing off" the AKs
• 5-fluorouracil (a chemotherapy agent): a cream that contains this medication causes AKs to become red and inflamed before they fall off
• Photodynamic therapy: this new therapy involves injecting a chemical into the bloodstream, which makes AKs more sensitive to any form of light.
• Laser, notably CO2 and Er:YAG lasers. A Laser resurfacing technique is often used with diffuse AKs.
• Electrocautery: burning off AKs with electricity
• Immune Response Modifier: topical treatment with imiquimod (Aldara), an immune enhancing agent
• Different forms of surgery

Regular follow-up after the treatment is advised by many doctors. The regular checks are to make sure no new bumps have developed and that old ones haven't become thicker.

Experimental treatments

In 2007, Australia biopharmaceutical company Clinuvel Pharmaceuticals Limited began clinical trials with a melanocyte-stimulating hormone called afamelanotide (formerly CUV1647) for mitigation of photodynamic therapy side effects in organ transplant patients.

Another Australian biopharmaceutical company, Peplin, is also developing a topical treatment for actinic keratosis. Formed in 1998 they are currently developing Ingenol Mebutate, which is the first in a new class of compounds and which is derived from Euphorbia peplus, or E. peplus, a rapidly growing, readily-available plant, commonly referred to as petty spurge or radium weed. The sap of E. peplus has a long history of traditional use for a variety of conditions, including the topical self-treatment of various skin disorders, such as skin cancer and pre-cancerous skin lesions. The company has recently redomiciled to the USA and is about to enter phase III trials with Ingenol Mebutate.
 

Because it interfaces with the environment, skin plays a key role in protecting (the body) against pathogens and excessive water loss. Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates. Severely damaged skin will try to heal by forming scar tissue. This is often discolored and depigmented.

In humans, skin pigmentation varies among populations, and skin type can range from dry to oily. Such skin variety provides a rich and diverse habit for bacteria which number roughly a 1000 species from 19 phyla.

Skin components

Skin has mesodermal cells, pigmentation, or melanin, provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation (UV) in sunlight. It also contains DNA-repair enzymes that help reverse UV damage, and people who lack the genes for these enzymes suffer high rates of skin cancer. One form predominantly produced by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be deadly. Human skin pigmentation varies among populations in a striking manner. This has led to the classification of people(s) on the basis of skin color.

The skin is the largest organ in the human body. For the average adult human, the skin has a surface area of between 1.5-2.0 square metres (16.1-21.5 sq ft.), most of it is between 2–3 mm (0.10 inch) thick. The average square inch (6.5 cm²) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.

Functions

Skin performs the following functions:

1. Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system.
2. Sensation: contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury; see somatosensory system and haptics.
3. Heat regulation: the skin contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. Dilated blood vessels increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat.
4. Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss. Loss of this function contributes to the massive fluid loss in burns.
5. Aesthetics and communication: others see our skin and can assess our mood, physical state and attractiveness.
6. Storage and synthesis: acts as a storage center for lipids and water, as well as a means of synthesis of vitamin D by action of UV on certain parts of the skin.
7. Excretion: sweat contains urea, however its concentration is 1/130th that of urine, hence excretion by sweating is at most a secondary function to temperature regulation.
8. Absorption: In addition, medicine can be administered through the skin, by ointments or by means of adhesive patch, such as the nicotine patch or iontophoresis. The skin is an important site of transport in many other organisms.
9. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.

Hygiene and skin care

The skin supports its own ecosystems of microorganisms, including yeasts and bacteria, which cannot be removed by any amount of cleaning. Estimates place the number of individual bacteria on the surface of one square inch (6.5 square cm) of human skin at 50 million, though this figure varies greatly over the average 20 square feet (1.9 m2) of human skin. Oily surfaces, such as the face, may contain over 500 million bacteria per square inch (6.5 cm²). Despite these vast quantities, all of the bacteria found on the skin's surface would fit into a volume the size of a pea. In general, the microorganisms keep one another in check and are part of a healthy skin. When the balance is disturbed, there may be an overgrowth and infection, such as when antibiotics kill microbes, resulting in an overgrowth of yeast. The skin is continuous with the inner epithelial lining of the body at the orifices, each of which supports its own complement of microbes.

Proper skin hygiene is important because unclean skin favors the development of pathogenic organisms. The dead cells that continually slough off the epidermis mix with the secretions of the sweat and sebaceous glands and the dust found on the skin form a filthy layer on its surface. If not washed away, the slurry of sweat and sebaceous secretions mixed with dirt and dead skin is decomposed by bacterial flora, producing a foul smell. Functions of the skin are disturbed when it is excessively dirty; it becomes more easily damaged, the release of antibacterial compounds decreases, and dirty skin is more prone to develop infections.

Cosmetics should be used carefully on the skin because these may cause allergic reactions. Each season requires suitable clothing in order to facilitate the evaporation of the sweat. Sunlight, water and air play an important role in keeping the skin healthy.

Oily Skin

Oily skin is caused by over-active sebaceous glands, that produce a substance called sebum, a naturally healthy skin lubricant. When the skin produces excessive sebum, it becomes heavy and thick in texture. Oily skin is typified by shininess, blemishes and pimples. The oily-skin type is not necessarily bad, since such skin is less prone to wrinkling, or other signs of aging, because the oil helps to keep needed moisture locked into the epidermis (outermost layer of skin).

The negative aspect of the oily-skin type is that oily complexions are especially susceptible to clogged pores, blackheads, and buildup of dead skin cells on the surface of the skin. Oily skin can be sallow and rough in texture and tends to have large, clearly visible pores everywhere, except around the eyes and neck.

The goal of treating oily skin is to remove excess surface sebum without complete removal of skin lipids. Severe degreasing treatment can foster an actual worsening of sebum secretion, which defeats the aim of the cleansing. A method of cleansing oily skin is to cleanse with a natural face cleanser formulated especially for oily skin. The cleansers pH should be 4.5 – 5.5, since the skin's pH value is approximately 5.4. Gel cleansers work best on oily skin. (see: surfactant) Oily skin products should contain very little natural oils. They should not contain waxes or other synthetic lipid agents that could aggravate the oily condition of the skin. A toning lotion should also be natural and have a pH of 4.5-5.5 and formulated especially to help balance and hydrate oily skin. Some cleansing products have lower concentrations of hydroxy acids, which remove dead cells from the upper levels of the stratum corneum. Those products should be used on a regular basis to work adequately.

In cases of excessive output of sebum, there have been anecdotal reports of successful control using dietary supplementation of Niacin (Vitamin B3) at a dosage of 500 mg to 1000 mg a day

Aging

As skin ages, it becomes thinner and more easily damaged. Intensifying this effect is the decreasing ability of skin to heal itself as a person ages.

Among other things, skin aging is noted by a decrease in volume and elasticity. There are many internal and external causes to skin aging. For example: Aging skin receives less blood flow and lower glandular activity.

Cortisol causes degradation of collagen, accelerating skin aging.

Photoaging

Photoaging has two main concerns: an increased risk for skin cancer and the appearance of damaged skin. In younger skin, sun damage will heal faster since the cells in the epidermis have a faster turnover rate, while in the older population the skin becomes thinner and the epidermis turnover rate for cell repair is lower which may result in the dermis layer being damaged.

Disease

Dermatology is the branch of medicine that deals with conditions of the skin.

Two abnormal conditions of skin pigmentation:-

• Leucoderma: skin pigmentation is lost(melanin) from smaller or larger patches at different regions of the body:exact cause of this disease is not yet known
• Albinism: complete loss of pigmentation of skin all over the body including hair, eyebrows, eye lashes, and even the iris. skin of such person appears pinkish because of the underlying blood capillaries. albinism is a recessive trait caused due to inheritance: an albino couple would get all albino children
   

• Timing of light (upset of normal circadian rhythms, seasonal affective disorder, sleep disorders)
• Intensity of light (photophobia, sunburn, skin cancer)
• Wavelength of light ( in lupus, urticaria )
• Rapid flickers in intensity of light may trigger or aggravate epilepsy or migraine headaches.
• Other effects may include vertigo, or chronic fatigue syndrome.

In rare cases individuals with solar urticaria (allergy to sunlight) can get a rash from fluorescent lighting or may experience disease activity in very photosensitive individuals with Systemic lupus erythematosus. Standard acrylic diffusers over the fluorescent lamps absorb nearly all the UV-B radiation and appear to protect against this.

In rare cases, fluorescent lighting can also induce depersonalization and derealization, subsequently, it can worsen depersonalization disorder symptomology. Research on these rare cases is very limited and cause and effect often cannot be duplicated.

Controlled application of artificial light can be used in a program of Light therapy to treat some disorders.

Associated Conditions

Ultraviolet radiation risk

Some fluorescent lamps emit ultraviolet radiation that in some circumstances can exceed safe levels. The Health Protection Agency of the United Kingdom has conducted research that concluded exposure to some compact fluorescent lamps (CFLs) for 1 hour per day at a distance of less than 30 cm can exceed safe levels. Touching the exposed bulb results in equivalent exposure to ultraviolet radiation as that of being in direct summer sunlight.

Skin and retinal cancers

Ultraviolet radiation emitted by fluorescent lighting increases an individual's exposure to carcinogenic radiation by 10 to 30 per cent per year, with an associated increased probability of contracting squamous cell carcinoma by 4 percent. Melanoma has been shown to not be affected by CFLs through normal use.

The constituent blue light of CFLs can aggravate retinal diseases in susceptible people, but it is unlikely to occur.

Migraine

Blue light, such as that emitted by CFLs, can aggravate migraine, and fluorescent lamps can cause eye-strain and headache. There is no available data on the existence of CFL-induced migraine, but there is anecdotal evidence of "problems" with blue light. The charity Migraine Action says its members suffer migraines induced by CFLs and there are many anecdotal reports of such occurrences.

Autism and Asperger syndrome

The SCENIHR report states that "people with Autism/Aspergers syndrome have reported problems which they attributed to fluorescent lighting", and any deleterious effects on sufferers of autism or Asperger Syndrome from CFLs cannot be dismissed.

Ménière's disease and Vertigo

The inner-ear condition Ménière's disease can be aggravated by flicker. Sufferers of vertigo are recommended to not use fluorescent lights.

Polymorphous light eruption

Polymorphous light eruption is a condition affecting the skin thought to be caused by an adverse reaction to ultraviolet light. Its prevalence across Europe is 10-20% of the population. Artificial light sources may provoke the condition, and CFLs have been shown to produce an eruption.

Chronic actinic dermatitis

Chronic actinic dermatitis is a condition where a subject's skin becomes inflamed due to a reaction to sunlight or artificial light. Its prevalence in Scotland is 16.5 per 100,000 population. There is evidence that CFLs worsen the condition.

Lupus

The autoimmune disease Lupus is exacerbated by CFLs.

Actinic Prurigo

There is evidence that Actinic prurigo is worsened by CFLs. This disease affects 3.3% of the general population.

Solar Urticaria

3.1% of the population suffer Solar urticaria, a skin disorder affected by ultraviolet light. Some patients are directly affected by CFLs.

Phytophotodermatitis

Phytophotodermatitis may be aggravated by the additional levels of ultraviolet light emitted by CFLs.

Additional risk for patients undergoing photodynamic therapy

Patients undergoing photodynamic therapy are at additional risk of adverse photosensitive reactions caused by CFLs.

Chronic fatigue syndrome

Self-reporting suggests that 21% of chronic fatigue syndrome patients experience sensitivity to light, and there have been no studies into the association between chronic fatigue syndrome and CFLs.

Cataracts

One cause of cataracts is exposure to ultraviolet light. Provided the level of UV emission from lamps is within safe limits, and the lamp a sufficient distance away from the individual, there should be no increased risk of developing cataracts.

Photophobia

Photophobia is a symptom of excessive sensitivity to light which affects 5 to 20% of the population. No studies have been conducted into the effect of CFLs on sufferers of photophobia, but there is the possibility for CFLs to affect sufferers.

Epilepsy

There is evidence that flicker can cause seizures in patients with photosensitive epilepsy, but there has yet to be any evidence to date attributing seizures to compact fluorescent lamps.

Dyslexia

Self-reporting suggests fluorescent lamps aggravate dyslexia. Tests show that dyslexic patients are unable to detect flicker emanating from light sources.