The disease can infect trees as young as 6 years-old, and infects trees throughout their lifespan. Diagnostic symptoms include crown yellowing and thinning, a distress crop of cones, red brown stained outer heartwood, and laminate decay (decay that separates along annual rings). The disease tends to occur in patches due to a primarily short range spread mechansism. Infected or decayed roots break close to the root collar forming “root balls.” Laminated root rot is frequently detected during ground survey when canopy openings and standing dead and fallen trees are observed. Signs of laminated root rot include the setal hyphae (tiny hairlike hyphae) between sheets of decomposing wood and also buff-colored mycelium on the outside of the roots.

Laminated root rot also known as yellow ring rot is caused by the fungal pathogen "Phellinus weirii". Laminated root rot is one of the most damaging root disease amongst conifers in northwestern America and true firs, Douglas-fir, Mountain hemlock, and Western hemlock are highly susceptible to infection with "P. weirii". A few species of plants such as Western white pine and Lodgepole pine are tolerant to the pathogen while Ponderosa pine is resistant to it. Only hardwoods are known to be immune to the pathogen.

Cyclaneusma (needle cast) is a fungal disease that is a part of the phylum, Ascomycota. It infects plants that are of pine classification. After infection by "Cyclaneusma", most pines do not display symptoms until 10 months after the initial infection. Symptoms include needles developing yellow spots, horizontal brown bands around the needles, swelling of needles, and off-white fruiting bodies formed on infected needles. Because "Cyclaneusma" is an ascomycete it produces two spore types, an asexual (conidiomata) and sexual (ascomycota) spore. Controlling "Cyclaneusma" has presented a challenge as the disease can survive on both living and dead needles during the winter months. Effective management methods include planting new pines in non-shaded, well drainable soil as well as spraying fungicide. "Cyclaneusma" Needle Cast is an important fungal disease because it directly impacts the commercial value of decorative pines as well as lumber.

The foamy bark canker is a disease affecting oak trees in California caused by the fungus "Geosmithia pallida" and spread by the Western oak bark beetle ("Pseudopityopthorus pubipennis"). This disease is only seen through the symbiosis of the bark beetles and the fungal pathogen. The bark beetles target oak trees and bore holes through the peridermal tissues, making tunnels within the phloem. The fungal spores are brought into these tunnels by the beetles and begin to colonize the damaged cells inside the tunnels. Symptoms of the developing fungus include wet discoloration seeping from the beetle entry holes as the fungus begins to consume phloem and likely other tissues. If bark is removed, necrosis of the phloem can be observed surrounding the entry hole(s). As the disease progresses, a reddish sap and foamy liquid oozes from entry holes, thus giving the disease the name Foamy bark canker. Eventually after the disease has progressed, the tree dies. This disease is important because of its detrimental effects on oak trees and its ability to spread to several new Californian counties in just a couple years.

Leaf rust is a fungal disease of barley caused by "Puccinia hordei". It is also known as brown rust and it is the most important rust disease on barley.

Pustules of leaf rust are small and circular, producing a mass of orange-brown powdery spores. They appear on the leaf sheaths and predominantly on the upper leaf surfaces. Heavily infected leaves die prematurely.

Citrus Black Spot is a fungal disease caused by Guignardia citricarpa. This Ascomycete fungus affects citrus plants throughout subtropical climates, causing a reduction in both fruit quantity and quality. Symptoms include both fruit and leaf lesions, the latter being critical to inter-tree dispersal. Strict regulation and management is necessary to control this disease since there are currently no citrus varieties that are resistant.

Hosts associated with "Geosmithia pallida" include a number of tree species, including oak and other hardwoods, pine and spruce trees, depending on the beetle vector. In this case, the western oak bark beetles target live oak trees of western United States. Beetles tend to attack stressed trees that are already weakened from drought or injury. Symptoms causing branch dieback and tree death also include a cinnamon-colored gum seeping from multiple beetle entry holes on the bole, followed by a prolific, cream-colored foamy liquid. These symptoms, as well as signs (entry holes, larvae, beetles) of bark beetles, are key factors in diagnosis. Necrosis of xylem and phloem tissues underneath bark can be observed.

Common Symptoms:

- Wet discoloration on bark

- Phloem necrosis

- Beetle entry holes

- Reddish sap oozing from entry holes

- Foamy liquid from entry holes

False melanose lesions are characterized by many small, tan, slightly raised lesions. The lesions are much smaller than the hard spot variety with an average diameter of less than 1 mm (.04 in).

They are found on unripe fruit and are difficult to observe later in the season. Unlike hard spot lesions, no pycnidia are present.

Wheat yellow rust ("Puccinia striiformis" f.sp. "tritici"), also known as stripe rust, is one of the three wheat rust diseases principally found in wheat grown in cooler environments. Such locations are generally associated with northern latitudes or cooler seasons.

As R.P. Singh, J. Huerta-Espino, and A.P. Roelfs say in their (undated) comprehensive review of literature on the wheat rusts for UN FAO:

"Although Gadd first described stripe rust of wheat in 1777, it was not until 1896 that Eriksson and Henning (1896) showed that stripe rust resulted from a separate pathogen, which they named P. glumarum. In 1953, Hylander et al. (1953) revived the name P. striiformis."

Needle cast diseases in general are somewhat difficult to diagnose simply because their symptoms are similar to low pH, poor nutrition, fertilizer or chemical burn, and even root rots. Correct diagnosis requires microscopic examination of the size and shape of the fungal producing ascospores. Unfortunately these fungal spores are produced quite infrequently; after the disease infects needles, it will not produce symptoms or additional spores until the following year. In addition, "Cyclaneusma" may not be the only fungus present on the diseased needles. Saprophytic fungi live on dead tissue and may therefore continue to worsen the infection on needles after they have fallen. Saprophytes will also be present if the needles were killed by fertilizer burn or root rots. Due to these obstacles, it is important to examine the spores directly after infection (while spores are being produced) in order to ensure that "Cyclaneusma" is indeed the pine’s cause of death.

A corn (or "clavus", plural "clavi") is a specially shaped callus of dead skin that usually occurs on thin or glabrous (hairless and smooth) skin surfaces, especially on the dorsal surface of toes or fingers. They can sometimes occur on the thicker palmar or plantar skin surfaces. Corns form when the pressure point against the skin traces an elliptical or semi-elliptical path during the rubbing motion, the center of which is at the point of pressure, gradually widening. If there is constant stimulation of the tissue producing the corns, even after the corn is surgically removed, the skin may continue to grow as a corn.

The hard part at the center of the corn resembles a funnel with a broad raised top and a pointed bottom. Because of their shape, corns intensify the pressure at the tip and can cause deep tissue damage and ulceration. The scientific name for a corn is "heloma" (plural "helomata"). A hard corn is called a "heloma durum", while a soft corn is called a "heloma molle".

The location of the soft corns tends to differ from that of hard corns. Hard corns occur on dry, flat surfaces of skin. Soft corns (frequently found between adjacent toes) stay moist, keeping the surrounding skin soft. The corn's center is not soft however, but indurated.

The specific diagnostic workup and treatments for corns may differ substantially from other forms of calluses.

Velvet disease (also called gold-dust, rust and coral disease) is a fish disease caused by dinoflagellate parasites of the genus "Piscinoodinium", specifically "Amyloodinium" in marine fish, and "Oodinium" in freshwater fish. The disease gives infected organisms a dusty, brownish-gold color. The disease occurs most commonly in tropical fish, and to a lesser extent, marine aquaria.

The single-celled parasite's life cycle can be divided into three major phases. First, as a tomont, the parasite rests at the water's floor and divides into as many as 256 tomites. Second, these juvenile, motile tomites swim about in search of a fish host, meanwhile using photosynthesis to grow, and to fuel their search. Finally, the adolescent tomite finds and enters the slime coat of a host fish, dissolving and consuming the host's cells, and needing only three days to reach full maturity before detaching to become a tomont once more.

People with diabetes face special skin challenges. Because diabetes affects the capillaries, the small blood vessels which feed the skin, thickening of the skin with callus increases the difficulty of supplying nutrients to the skin. Callus formation is seen in high numbers of patients with diabetes, and together with absent foot pulses and formation of hammer toe, this may be an early sign of individuals at an increased risk for foot ulcers.

The stiffness of a callus or corn, coupled with the shear and pressure that caused it, may tear the capillaries or adjoining tissue, causing bleeding within the callus or corn. Often, bleeding within a callus is an early sign of diabetes, even before elevated blood sugars may be noticed. Although the bleeding can be small, sometimes small pools of blood or hematoma are formed. The blood itself is an irritant, a foreign body within the callus that makes the area burn or itch. If the pool of blood is exposed to the outside, infection may follow. Infection may also lead to ulceration. Fortunately, this process can be prevented at several places. Diabetic foot infections are the leading cause of diabetic limb amputation.

Once pederin is on the skin from the initial beetle contact, it may also be spread elsewhere on the skin. "Kissing" or "mirror-image" lesions where two skin areas come in contact (for example, the elbow flexure) are often seen. Washing the hands and skin with soap and water is strongly recommended, if contact with a rove beetle has occurred.

Initial skin contact with pederin shows no immediate result. Within 12–36 hours, however, a reddish rash (erythema) appears, which develops into blisters. Irritation, including crusting and scaling, may last from two to three weeks.

One study reported best results with a treatment regimen that combined topical steroids with oral antihistamines and antibiotics. The authors hypothesized that antibiotics were helpful because of the possible contamination of skin by pederin-producing bacteria.

Paederus dermatitis (also called linear dermatitis or dermatitis linearis) is skin irritation resulting from contact with the hemolymph of certain rove beetles, a group that includes the genus Paederus. Other local names given to Paederus dermatitis include spider-lick, whiplash dermatitis, and Nairobi fly dermatitis.

The active agent is commonly referred to as pederin, although depending on the beetle species it may be one of several similar molecules including pederone and pseudopederin.

"Blister beetle dermatitis," a term more properly used for the different dermatitis caused by cantharidin from blister beetles, is also sometimes used to describe paederus dermatitis caused by rove beetles.

Sporotrichosis can be diagnosed in domestic and wild mammals. In veterinary medicine it is most frequently seen in cats and horses. Cats have a particularly severe form of cutaneous sporotrichosis and also can serve as a source of zoonotic infection to persons who handle them and are exposed to exudate from skin lesions.

As the common name for this condition implies, it causes itching or a burning sensation in the groin area, thigh skin folds or anus. It may involve the inner thighs and genital areas, as well as extending back to the perineum and perianal areas.

Affected areas may appear red, tan, or brown, with flaking, rippling, peeling or cracking skin.

The acute infection begins with an area in the groin fold about a half-inch across, usually on both sides. The area may enlarge, and other sores may develop. The rash has sharply defined borders that may blister and ooze.

Tinea cruris does have similar symptoms to Inverse psoriasis.

Sporotrichosis (also known as "rose gardener's disease") is a disease caused by the infection of the fungus "Sporothrix schenckii". This fungal disease usually affects the skin, although other rare forms can affect the lungs, joints, bones, and even the brain. Because roses can spread the disease, it is one of a few diseases referred to as "rose-thorn" or "rose-gardeners' disease".

Because "S. schenckii" is naturally found in soil, hay, sphagnum moss, and plants, it usually affects farmers, gardeners, and agricultural workers. It enters through small cuts and abrasions in the skin to cause the infection. In case of sporotrichosis affecting the lungs, the fungal spores enter through the respiratory pathways. Sporotrichosis can also be acquired from handling cats with the disease; it is an occupational hazard for veterinarians.

Sporotrichosis progresses slowly – the first symptoms may appear 1 to 12 weeks (average 3 weeks) after the initial exposure to the fungus. Serious complications can also develop in patients who have a compromised immune system.

Intense rubbing can cause a blister, as can any friction on the skin if continued long enough. This kind of blister is most common after walking long distances or by wearing old or poorly fitting shoes. Blisters are most common on the hands and feet, as these extremities are susceptible while walking, running, or performing repetitive motions, such as joystick manipulation whilst playing certain video games, digging with a shovel, playing guitar, etc. Blisters form more easily on moist skin than on dry or soaked skin, and are more common in warm conditions. Less-aggressive rubbing over long periods of time may cause calluses to form rather than a blister. Both blisters and calluses can lead to more serious complications, such as foot ulceration and infection, particularly when sensation or circulation is impaired, as in the case of diabetes, neuropathy or peripheral artery disease (PAD).

A blister may form when the skin has been damaged by friction or rubbing, heat, cold or chemical exposure. Fluid collects between the epidermisthe upper layer of the skinand the layers below. This fluid cushions the tissue underneath, protecting it from further damage and allowing it to heal.

Tinea cruris, also known as crotch itch, crotch rot, Dhobi itch, eczema marginatum, gym itch, jock itch, jock rot, scrot rot and ringworm of the groin is a dermatophyte fungal infection of the groin region in any sex, though more often seen in males.

The lesions are most frequent on the lower limbs, but may occur anywhere on the body, including the hands, arms, torso and even the neck. They may vary in number and erupt in mass numbers.

They consist of irregular patches of orange or brown pigmentation with characteristic "cayenne pepper" spots appearing within and at the edge of old lesions.

There are usually no symptoms, although there may be some slight itching, but there is no pain.

The eruption may persist for many years. The pattern of the eruption changes, with slow extension and often some clearing of the original lesions.

Schamberg's disease, or progressive pigmented purpuric dermatitis, is a chronic discoloration of the skin which usually affects the legs and often spreads slowly. This disease is more common in males and may occur at any age from childhood onward. This condition is observed worldwide and has nothing to do with race or ethnic background.